While quite shocking, that's not the problem with eBay.
A few years back I bought a very rare riser over eBay (turned out the seller lived about a mile from me - who knew?) paid, got the riser and was happily shooting it when my mother sent me a link and said "hey look, there's another one just like yours!"
Just like mine.
It was the same ad, from a different seller - the whole thing had been copied and pasted as a scam!
Ironically, the ad included the serial number, so I could easily prove to eBay that it was a fake.
Caveat emptor, indeed