You find an old-looking piece of United States currency and wonder, can I sell this on ebay? Of course you can! And here are some pointers on how best to find a good home for your note:
1) Find the right category for the note. Many notes fail to be sold or draw a much lower price than they should because they get miscategorized, turning up in the wrong place. For example, because one thinks it to be old it must be "obsolete" and so one jams it in the "Obsolete Currency" category. There are many sorts of currency one might think of as "obsolete" because they are no longer printed and seldom to never seen in circulation. However, that category is actually for older (and usually larger) sized notes issued by individual banks and even merchants from the Colonial period until about the Civil war time. Not everything out of print belongs there. The Ebay categories (as I write this) stand as follows:
a) Replicas & Reproductions: Use this for anything you might recognize as being not an original note of actual monetary value, but rather some sort of reprint. Current laws call for reprints to be of a different size than real notes, so as to avoid confusion with real notes or any charge of counterfeiting. That only applies to notes that are still legal tender, which would be just about anything from about 1861 onward (a few truly "obsolete" notes did continue to be printed for some years during and after the war. Older notes, such as colonial notes, often get reprinted in actual size, but on a strong, thick kind of yellowish parchment paper. $1,000 dollar notes from 1840 with a serial number of 8894 are reproductions, and would also go here.
b) Bank Checks: Bank checks are ordinary cashable checks (sort of like paychecks, and some of them probably are actual paychecks) that are issued by banks.
c) Colonial Currency: The famous (once infamous, as in "not worth a ...") "Continental" comes in a variety of denominations and was issued by the American government back in the latter part of the 1700's to pay for the revolutionary war. In those days, individual states also issued paper money, often in units of money different from current money (e. g. Shillings or in Spanish Milled Dollars). Basically, anything from the 1700's to early 1800's belongs in this category, except of course reproductions of the same.
d) Confederate Currency: This is always easy to identify since it will say on it "The Confederate States of America" and appears in a size noticably larger than the money we use today (actually about the same size as the older "large size" currency).
e) Errors: Use this for notes that were not printed correctly. Do not waste time with notes that have simply been damaged in some way (some forms of damage, such as bleaching, will even change the color of the ink, but that does not qualify as an error note), but with evident problems that occured with the printing, for example missing the seal or with serial numbers that differ from each other by one digit, or part of the back printed on the front side, and so forth.
f) Fractional Currency: Mind-boggling as it might well seem, the U. S. actually used to have paper "coinage" of denominations of 3, 5, 10, 15, 25, and 50 cents. These were issued back in the 1860's and 1870's as a substitute for coins that were often in very short supply. These are somewhat smaller than the current paper money, and some of them, especially the earliest issues, actually look more like postage stamps, but unlike stamps they were issued without the "glue" on the back that stamps always necessarily have.
g) Large Size Notes: Up until 1929 when paper money the size we have it today was introduced, all US paper money (other than the actually smaller Fractional Currency) was actually a larger size than it is today. These notes are often very colorful and come with designs often quite different from the contemporary designs. There are three exceptions to this which, though being large size, actually belong to other categories. One is the "Obsolete Currency" issued by banks and merchants from the colonial days until shortly after the Civil war, another is Confederate Currency, and the last is "National Bank Notes."
h) Military Payment: These notes will actually say "Military Payment" on them and often feature (usually anonymous) female visages on the front instead of the more usual and expected "dead Presidents" one finds on most other currencies.
i) Novelty: This is a category for what usually isn't really even money, though real currency with some different picture applied over the visage (to replace its "dead President" with someone else) would also belong in this category. Other kinds of money that might go here would be that with limited and specialized but actual value, for example Disney Dollars which really can be spent in Disneyland, but nowhere else, political or other parody currency, play money, joss paper (looks sort of like money, but usually made from cheap rice paper and bearing a Chinese emperor and ridiculously large denominations, used by being ritually burned in sacrifice by the Chinese on behalf of their dead ancestors), and (perhaps) private currencies such as the Liberty Dollar (though that might be a reasonable candidate for the category of "Other").
j) Small Size Notes: Starting in 1929 (but dated 1928 in most of its earliest series) the money which is the same size as that used today belongs in this category. Excluded from this would be Novelty and National Bank Notes, which have their own categories. But apart from those two categories, if it has the same size as today's money and a similar look to money today, then it goes here.
k) National Bank Notes: These notes come in two basic categories, Large Size Notes and Small Size Notes. The large size notes will actually say "National Bank Note" on them somewhere, and also give the name of some issuing bank, such as the "Second National Bank of Boston" or whatever. The small size notes say "National Currency" at the top, have a small brown seal (the same size as the green treasure seal on today's currency) at the right side, four different signatures, and the name of some national bank on the left side. The scrollwork is also simplified, streamlined, and compressed a bit to make room for all this information. There will also be a black number written vertically on each side (digits sideways on the left side but upright on the right side) which are the particular banks charter number. If the brown seal is larger than today's treasure seal and instead of these numbers there are four black instances of some letter ("A" to "L"), diagonally placed two to each side of the note, do not put the note in this category but in the regular "Small Size Notes" category, for that is actually what is called a "Federal Reserve Bank Note," even though it does not say that anywhere on the note itself.
l) Obsolete Currency: This refers to the period from the Colonial era until the Civil War during which this country had no central bank, but individual banks (and some merchants) issues their own money.
m) Collections, Lots: Use this for large piles of currency (or currency combined with other things) which you have no intention of itemizing singularly. Generally, by not itemizing it you will not get as much for it, but on the other hand a large pile of stuff can be sold all at once as a single ebay listing, and that may well be cheaper for some things that may not be worth very much.
n) Other: Generally, you should avoid this category, except for some really oddball items that don't fit into any of the above categories (I did say that private currencies, such as the Liberty Dollar, might go here, however).
2) Having identified the category to put it in, next you need to describe it. Here are the things you need to include in a description:
a) What kind of note it is: This will usually be written across the top of the note, but may in some cases be elsewhere. For Large and Small Size Notes and National Bank Notes in particular, it is important to identify the kind of money that it is. In the case of the Large Size Note, it will say somewhere, such phrases as "Silver Certificate" "Gold Certificate" "Legal Tender" "Demand Note" "United States Note" "Treasury Note" "Gold Coin Note" or "Federal Reserve Note," or the like. Find that phrase and copy it verbatim from the note into your description, as that is the best way for someone looking for your note to find it using a search. Small size notes are (generally) color-coded. With only a couple exceptions, they also say what kind of note they are. Those exceptions are the National Bank Note and the Federal Reserve Bank Note (which both read "National Currency" across the top and both have a brown seal). In addition, the Gold Certificate says what it is, not at the top, but over a yellow treasury seal at the left side. Everything else will either say "Silver Certificate" (having a blue seal), "United States Note" (having a red seal), or "Federal Reserve Note" (having a green seal) across the top.
b) What denomination the note is. It often works best to use the dollar sign and digits (without comma unless included on the numeric denomination of the note itself, e. g. "$20 note" or "$5000 note" or "$10,000 note."
c) What series year the note is: Look for a year on the note. Oftentimes, there may also be a letter associated with the year, either right after it or right under it, for example "1963 A". If there is no such letter, it can sometimes be helpful to mention that it is "no letter." Make sure you include that year (and letter, or lack of a letter). Some older notes (and Confederate series) have an actual date, which should be provided in the description in full. Such a date is typically not actually the date of the note, however.
d) What condition the note is in. Do not call it "Crisp Uncirculated" unless it really does look like it was newly printed, the paper looks fresh, without folds, wear and tear, or any damage, corners are sharp, and you can almost "feel" the designs on the paper with your fingers. You may call it "Almost Uncirculated" or "AU" if it has only one or two folds, looks like it has been in your wallet for a week (having come straight new from the bank), and still seems quite new, though discernably less than absolutely perfect. Anything below this must be called "circulated." Call it "Very Fine" or "VF" if it looks about as bad as it can get without actually seeming to be soiled, damaged, and still has real eye appeal despite noticeable wear, folds, soft corners. If it looks like it's been kept crumpled in the toe of a soldier's boot for the whole war, call it circulated and don't grade it beyond that. If you don't trust your grading judgement, you may just present a picture of it and invite the buyer to decide for himself, but this is kind of annoying, in fact almost as annoying as a misgraded note. Better: Put your estimate of the grade (e. g. "VF") in the "condition" field and then in the text say "I think this note is Very Fine, but I am not a professional grader; please judge for yourself." It is better to estimate low than high, if you can't be sure between two possible grades or conditions for it. Finally, hold it up to the light and see if it has any tears or "pinholes" (such as made by stapling the note to something). Anything of this sort MUST be reported in the description, even though it lowers the sale price, since to fail to do so may result in an unsatisfied customer and having to pay money back, have the note returned, or else end up with negative feedback. The same goes for stains, marks, writing, and so forth. It is not enough that it might well be seen in the picture.
e) If it is a wartime note. Some silver certificates dated 1934, 1934 A, and 1935 A will have a yellow seal on the right side (and WITHOUT the words "Gold Certifiate" over it), but blue serial numbers. These notes were used specifically during the North African campaign during the war, though no mention is made of that on the note. Make sure you describe such a note as a "North Africa wartime note." Similarly, some Federal Reserve Notes, again dated 1934 or 1934 A (and $1 Silver Certificates dated 1935 A) will have a brown seal and the words HAWAII on each side and in hollow letters across the back. These notes were used specifically during the war in Hawaii for fear the Japanese might take it over and confiscate large sums of American money. Make sure you describe such a note as a "Hawaii wartime note." Wartime notes always bring a premium over regular notes of the same issue, sometimes a substantial premium.
f) Anything else interesting about it as you may discern, for example if it has a star (call it a "star note") at the end (or beginning in some cases) of the serial number, or if the serial number seems interesting in some manner. There is no need to provide the serial number unless there is something interesting about it, for example an unusually low or high value, all digits the same, or counting up or down, or end-to-end palindromic (called a "radar note"), or otherwise memorable. If it is an error note, it helps to provide a short verbal description of the error, e. g. "unmatched serial numbers" or "upside-down back" or "missing treasury seals." If you happen to know what "mule note" is, or a "web note," or the like, you may mention that as well if they apply. If you have two or more notes with consecutive serial numbers, by all means mention that. Such notes may either be sold as a lot (and you don't need to use the "Collections, Lots" category for this), or individually (but if offered individually, still say that they come from a set of consecutive serial numbers and then always offer more than one adjacant number from this series at any given time).
g) Get a good picture of the note. A fuzzy and unclear picture limits the likelyhood of sale, or of getting a good price. No picture is even worse. Some of the best pictures are obtained by using a computer scanner. Be sure to set it to the maximum resolution and to color. There are also various currency imaging houses, such as Activa or Vendio which can also take beautiful pictures of what you have to sell.
3) Some notes may well be unusual in circulation today, but actually quite common and incapable of fetching much return, no matter how well presented. Most common in this category are low/medium grade United States notes from series 1953 and 1963 (any letter or none), and Silver Certificates from series 1957 (any letter or none). Chances are, the price over face of the note will not be enough to cover the cost of offering it on ebay. Such notes can be sold of course, and generally are most productively sold as lots, e. g. "Lot of 10 Series 1953 B $5 United States Notes, VF to AU condition."
4) Don't be afraid to offer notes that are not all that old, or else seem to have nothing "special" about them, especially if they are very high grade. Such "plain Jane" notes, so very common to begin with, often end up being rarer in the long term (particularly in the uncirculated condition) precisely because they are not considered very interesting. Think of the original 1883 Liberty Head nickel. The first million or so minted did not have the word "cents" on them and so became a most interesting variety, whereas the many more millions minted that year with the word "cents" were regarded as common, like all other Liberty Head nickels, and now are actually far scarcer than the originally much rarer version without "cents." You would be surprized by just how many notes are actually much rarer in the high grades as "plain Jane" notes than as "star notes," "mule notes," "web notes," etc., especially the issues of the past 40 years or so.
May you have all manner of luck and profit in selling your currency notes on Ebay!