(Note that this was written before the postage rate increase of May 14, 2007, so as you read please know that the priority rates are going up and there is an additional class of mail for packages. Consult with your post office if you're unsure about how you should ship, then when I understand the new rates better myself, I'll be back with an update. Thanks for reading! Susan, my52cents)
It's hard to argue with using USPS Priority Mail to ship ebay packages. The service is fast, generally efficient, and the United States Postal Service actually provides the Priority Mail envelopes and boxes for free! The question arises, though, about when to use the Priority Mail Flat Rate boxes. Are they always a good deal? They are if you use some general guidelines and common sense.
Priority mail rates depend on two factors - the weight of the package and its destination, or just how far the package will travel. When deciding which Priority Mail box or package to use, consider the following. (Note that USPS Priority Mail is only available for packages shipped in the United States to any United States address, including APO or FPO addresses.)
First, $4.05 is the cheapest Priority Mail rate. A flat rate envelope is always $4.05, no matter the weight, so use that when the item will fit into the flat rate envelope. That's the best deal you will get.
Priority Mail flat rate boxes cost $8.10 to ship.
Any package up to 1 pound is always $4.05 for Priority Mail, so never use a flat rate box if the package weighs under 1 pound. In fact, if your packed item weighs from 1 pound up to 2 pounds, do not use the flat rate box because the cost in a non-flat rate box will calculate to between $4.05 and $8.10, the shipping cost of the flat rate box, depending on the destination. (In other words, if you put it in the flat rate box, expect to pay the entire $8.10 even if the package weighs less than 2 pounds and is being shipped across the street!).
If it's over 2 pounds and will fit in the flat rate box, go with the flat rate box. The marked flat rate boxes (note that there are two flat rate box sizes) cost $8.10 to send for however much you can stuff inside, anywhere you send them. It's a great deal for smaller to medium-sized, heavier items, anything over 2 pounds (maximum weight allowed is 70 pounds).
If it's over 2 pounds and won't fit in a flat rate box, you should use a different Priority Mail box or envelope and either calculate postage based on zip code (use the ebay shipping calculator in your item listing) or choose an amount that will cover, or almost cover, shipping to the distance/zone farthest from you (most expensive). Sometimes it will be sent closer so will cost less, sometimes it may be far away and cost a little more, but generally it averages out if you ship several things that way. Shoppers seem not to like having to calculate, although I personally think the shipping calculator is a super tool and keeps shipping costs fair.*
Note that the post office has Priority Mail Tyvek envelopes in sizes from small to quite large. If you're sending something large and soft, perhaps a bulky coat, consider using the huge Tyvek envelope to keep your shipping weight down. I use these to mail shoe boxes with shoes. (I wrap the shoe boxes in bubble wrap, put them in the Tyvek envelope, and they travel fine.) It has the Priority Mail marking and I don't have to pay for the weight of the Priority Mail box!
So, where might one find these free Priority Mail containers? Visit the USPS web site home page (add a dot com after USPS). Under Shipping Tools click on Supplies to find the entire selection of all the mailing supplies the postal service has available. Choose Priority Mail to see that selection and note that all of the items that do not include prepaid postage are available at no charge. Order directly from the site and the supplies will be delivered to your door, again at no charge, within a couple of weeks. Additionally, ask at your post office as most will have a variety of shipping boxes and envelopes on hand.
A related topic is Delivery Confirmation (DC). Keep in mind that DC is a necessity when using Paypal, as a protection for you, the seller, in case there is ever a dispute about a shipment. DC does not track a package, but its purpose is to confirm delivery of the package, so never, never ship without it! The good news is that when using Paypal to purchase and print postage, Delivery Confirmation is always free when you choose Priority Mail. If you take the package to the post office and pay for postage there, you will have to pay extra for the Delivery Confirmation, so consider using Paypal to purchase and print postage for all of your ebay postage needs, and especially for shipping Priority Mail. What a great tool to help keep shipping costs down - great for the buyer as well as the seller. And the service is provided by Paypal, you guessed it, at no additional charge. Free is good!
As mentioned before, it's hard to argue with using USPS Priority Mail to ship ebay packages, and hopefully this explanation has made that clear. Happy selling and happy shipping!
(*Note that during ebay Live it was announced that soon items with shipping calculators will show the actual shipping cost already calculated based on the buyer's zip code when the item appears in a search. Great news for ebay shoppers and sellers alike! )