Paypal's operating rules may have changed, but I've similarly been bitten by money lost due to Paypal.
Here's how the scam works: someone buys something from you on eBay, pays you via Paypal. You diligently send off the good, and delivery confirmation shows it was received. The buyer waits till the last day possible to report the item as not received, Paypal puts your account in the red and you're stuck with the bill.