I had this a few years ago re: eBay.
I was after a Mercedes C Class and was watching quite a few on eBay and two specific ones are of note:
1. Where I bid on the car and won in the end - but then the seller refused to sell it to me claiming that it had gone too cheaply and he wanted more - so refused to sell. eBay could do nothing as the seller claimed to eBay that the vehicle was wrecked.
2. Where a fully specced that I was bidding on and the price was cheap (around £900) and suddenly all these new bidders appear (just registered) and the price is now £2000. I reported the seller as his mates were shill bidding for the item to bump the price up.
Don't get me wrong - eBay is a wonderful tool for viewing, buying and selling everything - but when it comes to older cars there are some real wankers out there.