Maybe this happens all the time, but I was a little surprised to discover that I'd purchased a fake pair of PX200s from eBay.
I wonder how many people have bought these fakes, and without a valid pair to compare to, just thought, 'wow, these just kinda suck...'. My coworker owns a pair, and we did a side by side comparison, and the differences in SQ are night and day. Build quality is more similar, but big differences are visible. Different texture in injection molded plastics, fakes are slippery and cheap feeling. Small things like bits of thread hanging out from seams, those type of things.
Anyway, if you plan to buy some on eBay and the picture has them in a little anti-static envelope, look closer at the details, and ask the seller about their return policy, etc.
Some details -
Cheap looking yellowish hinge:
Ill-fitting metal headband:
Baggy fabric on phones:
