With Paypal, if the customer funds their Paypal account with a credit card then it's flawed. They pay by Paypal which comes off the card. You get guaranteed funds from Paypal, you send the goods, customer receives the goods, customer tells credit card it's an unauthorised transaction or goods never arrived, credit card company reverse the transaction and customer gets his money back including a new wheel, and Paypal pursue you for the money they have to pay back. Removing your funds from Paypal doesn't work as they take you to court apparently. This one is more common in the UK.
Same thing with a stolen Paypal account. If it's unauthorised then Paypal will eventually return the funds to the rightful owner and pursue you for the money. This one is more common from overseas.