I am actually quite picky and choosy in what I buy off eBay, therefor, I very rarely get scammed.
But, it does happen.
One time, I bought several 1950s and 1960s Hall-of-Fame cards off a guy who had a very good rating. That week, however, he had a very bad week - shortly after I ordered his cards, I began noticing a ton of negative feedbacks, like within hours of my own purchase. I wait a few days. His negatives keep piling. I have no cards.
I send him a message. No reply. I send another message. No reply.
I open a case on all of the cards. Almost immediately, he messages me, telling me the cards are now in the mail.
A week goes by. Still nothing. I message him. No reply. At the time, eBay had a policy that so much time had to guy by before the case file was taken to the next step if no response came. Every day until that last day, I constantly messaged the guy. Still no reply.
By now, his negative feedbacks are to legendary numbers. By this time, the guy literally has more negative than positive - all those negatives from the last three weeks, and each one telling the same story I am.
By now, I have hit the next step, take it to the next level - and within two hours, he claims he has sent the cards, and has the tracking information to prove it. I tell him to prove it. After that, I never heard from him again.
eBay refunded my money, gave me a voucher for so much off my next purchase and two weeks later, that guy's account was completely closed.
Another time, I bought a 1956 Mickey Mantle off a guy with an extremely good rating. I get the card a couple of days later, pull it out of the sleeve...and find it is a fake. I've been collecting old baseball cards for quite some time, I know the feel of them by heart. I could tell immediately, that was not a real card.
I sent a message to the guy, telling him so. He told me that, indeed, much to his chagrin, it was a fake. The guy had previously dealt only in hockey cards. He had bought several high end baseball cards from the 1950s from a guy who claimed they were real. The guy who sold the cards to me did not know this...until a couple of days before I messaged him and several other buyers had emailed him with the same complaint. Because of the volume of cards he had sold that week, he had not a chance yet to inform and refund everyone who bought those cards. The real tragedy was that the card I bought was actually one of the cheaper of those bunches - I remember a 1933 Goudey Babe Ruth and a T-206 Ty Cobb being amongst the many cards he had sold during that period.
He went back to selling only hockey cards.