Negotiated a deal with ebay seller for a 1959 Willie Mays Bazooka box for around 1k (it was a number of years ago). He turns around and tells me he is selling it for a friend and his friend doesn't want him to sell it to me (even after explaining to his friend that we already had a deal and he thought it was a reasonable price at the time). The guy seemed legit. A week later it is listed as an auction on ebay again (different seller - original owner? I was really pissed and was determined not to bid more than the 1k the original deal was for. I didn't and ended up being the under bidder
Probably needless to say - I have not seen another.