With the flow on eBay of big E Levi's, original vintage (pre-1971) or LVC repro, has appeared the usual downside to the popularity of any item: the Counterfeit item (in this case, again as usual, Asian).
Buying vintage Levi's can be tricky for the layman, considering the lack of expertise may be on both sides: the buyer AND the seller. That's why it's necessary to ask the seller as many questions as you need to ask. And if you're not a pro and are not sure what you're buying, or whether the seller is really knowledgeable in the area of vintage denim or not, only bid up to the price you'd pay for the jeans according to their physical appeal to you, NOT to what you think they might be worth.
Most of what authenticates and dates a pair of jeans is in the details: the color of thread used, the position of the patch on the right hip and what it says, the size of the "big E" tab and whether it carries the "registered" logo (circled R), LEVI'S on both sides or not; the shape and size of the pockets, etc, etc... Once again, the trained eye will immediately recognize a pair of vintage Levi's from afar, and will likely be able to make out the time slot it was made in. The same goes for the recent LVC repros, US- or Japanese-made. LVC (US) has purposely made inaccurate copies of their own products (denim quality, shape & size of pockets, thread composition & color, size of, & lettering on red tab, general appearance of final product...), while presenting them as "point-by-point recreations of the original models". As far as I'm concerned, they outta get whacked in the face with a misleading publicity trial for lying so blatantly to a customer base obviously way more specialized than they are in their own past products, but Levi's recent tradition (since 1984) of using their history as a maker of decent and mythical clothing to publicize and hustle low-quality clothing is another topic... As far as I know, the best and most accurate repros around are those licensed to LVC Japan. The lemon stitching is usually used in the right places, the pockets are pretty much positioned correctly, the red tabs they use are the longer more accurate type, the denim has the correct blackish navy hue; even the apparent imprecise stitching is closer to what you'd get in a pair of Levi's before the '60s. Unfortunately, unless you're a very standard (smaller) size, and have connections in Japan, it'll be very hard to impossible to find a pair.
Which leads me to the main topic of this guide: the recent surge of Thai fakes, appearing daily under the "vintage big E 501 Levi's" search. I noticed this around 2006, out of a seller from Osaka, Japan. At first, the jeans they sold looked like really well worn vintage 501s, as if they'd found dozens of them locked up in a mine somewhere for years, after elegant miners had fortunately spent years wiping their palms on the right places (thighs and butts, mostly), without ever wearing them out to the point of making holes. So the jeans were sold as "vintage" while obviously being asian copies, but they looked good, and seemed to be of quite good quality denim. The second (and current) wave that appeared on eBay came from the same sellers, as well as others based in Thailand: the Thai fakes! While the fabric itself doesn't look too bad, the construction is of a way lower grade, and several details blow the whistle on them:
-a redline selvage in the middle of the back belt loop,
-a redline selvage on the change pocket, visible from the outside, not folded and stitched inside the pocket like on the originals. Other variants do have the selvage on the inside, but sewn with a double stitch instead of the normal single stitch.
-leather patches are usually centered on the right instead of being on the far right of the waist, usually of a smaller size, and in the weirdest colors, from off-white to dark brown, or even navy, black, or red.
-if an inside care tag is shown, you can sometimes spot typos or just broken English. They'll usually claim "Made in USA", but in a font never used by Levi Strauss C°.
-a more discreet, but still visible break in the back pocket top stitch (along the line you usually look at for double- or single-stitching). The fabric is folded under the parallel stitches, and let out near the edges of the pockets. On original vintage or repro, this serves to secure these edges with rivets. On these Thai fakes, there may or may not be rivets, but the fabric let out usually sticks out far, which is visible particularly when the jeans are faded. In the following pic, it goes all the way down to the red tab
-the red tab: usually very small, and added on without much care. You can see someone unstitched the old tab, replaced it with the current reading "LEVI'S", and stitched over the old seam, so you know it's been added outside of the factory and initial manufacturing process.*
-more difficult to see, the rises of these jeans are usually lower than normal, to follow the current trend, and perhaps simply because they were cut off Thai models.
As you can see, most of these features can easily be verified, and could help you avoid spending your money on mass-produced fakes.
*I've learned through research that Thai law is much more lenient for vendors than for manufacturers, although the Thais certainly aren't known for tough enforcement of copyright / intellectual property laws in general. There are quite a few manufacturers of fake Levi's, some also manufacturing their own legitimate brands. So it seems in some cases, to protect the factory from scrutiny from the authorities, these manufacturers produce "unmarked" jeans, for smaller workshops to sew labels on later, in more discreet settings, where they can also be hand-distressed, or lent to a local trustworthy derelict to break them in, by actual wear (true story!). The jeans then end up by the dozens on vendors' stalls on street markets, and in some specialized stores. Apparently small vendors risk little more than getting whipped with a bamboo stick in public, and/or their merchandise and money confiscated (stolen) by the local police. The local labor being so cheap explains how some eBay sellers find obvious interest in selling $5-10 jeans around $59-79 as BINs, when originals would easily get bids upwards of $200 (usually around $500-1000)