Most often "Legit" (meaning from the real factory) clothing being sold in Lhasa does have some kind of fault. It usually goes "out the back door" because it did not meet the quality control standard demanded by the international company. However most of the time these faults cannot be found or are very minor - like a missed stitch or something like that.
It is getting harder and harder to tell real from fake now - but if you know your brand and the item you want you can usually tell the difference.
The other issue that goes on - is that the "real" factories run overtime and produce the same "legit" item (same cut, same features etc) but they sometimes use cheaper fabric or cheaper features (zips etc) So this makes picking real from fake even more complicated.
Hint: nearly all ARCTERYX brand clothing in Lhasa is fake. Sometimes you can find original PATAGONIA brand items but most are fake. Nearly all NORTH FACE brand clothing in Lhasa is fake but some of the fakes are quite good!
You usually find out if it is real or not 1 year (or less) later when your garment starts falling apart or leaks like sieve!!