Is this his first pin purchase? Maybe he buys a lot of stuff on ebay and he's used to that Paypal guarantee and safety. Once he play tests it he'll probably feel more comfortable with the purchase. I agree that a hardcore legal document would make me feel that the seller was trying to hide something and protect themselves. But a simple hand written bill of sale having the names of the parties, machine name, serial number, price, and saying that the buyer tested it before leaving and is satisfied, sold as-is, no warranty would be alright.