Just extending Foxy's idea/suggestion, could you not have some sort of document for the customer to sign saying something like

"I have inspected the item, paid $xxx cash to "I'm the best seller in the world" as I am happy with it's condition and have now taken possession of it."

dunno - something like that would have to carry some weight...

Of course you would need to verify iot was their signature, hence where Foxy's suggestion comes in - a photocopy of BOTH SIDES of their Driver's Licence.