Its easy to prove that a domian has changed hands. I think you will win if it is disputed. What i always do when someone is paying me for something with paypal is not just simply give them the email address. Go in and create an invoice and have it sent to the buyer. Make sure you put exaclly what you are selling on the invoice. And have paypal will send them the invoice. That way if there is a dispute And you give them whatever they were buying you are good. This guy can say he bought anything for that 1000 bucks without an invoice.