I once bought an 8-bit VGA card from an Ebay seller. I paid for the card plus shipping. However, when the card arrived, it was a 16-bit card. I contacted seller who said, no problem, return it and he'd send the right one. I paid to ship the card back to the seller and the seller acknowledged he received the card but never sent the replacement. I contacted Ebay who opened an investigation. The first thing they did was put a hold on his money. He contacted me saying tell Ebay to release his money and he would send the card. I said, send the card and I would have Ebay release the money. In the end, Ebay decided in my favor so told me to provide proof that I had returned the item. All I had for proof was an email from the seller saying he had received the item I returned but that was NOT good enough for Ebay.
In the end, I was out the money I spent to buy the item (which Ebay kept) plus shipping in both directions. The seller still had the item to sell again and lost no money. Pretty screwed up transaction all-in-all.