It happens as a buyer, I buy expensive antique glass and have more than once had to fight with ebay to have the purchase refunded because it was not as advertised, or worse having a seller ship a piece that was previously broken and then turn around and try to claim it was the post office and defraud them.

so I understand paypal's and ebay's stance 1. They are up against CC companies who will side with their customer 2. A market suspected of selling fraudulent goods fails quickly 3. Sellers enter the agreement knowing full well there is a risk of a bad buyer and they will lose in the dispute.