@AlbertoT:
A real evidence? I don't know what would happen if Paypal was gone after some years. Anyways, from what I understand Paypal now operates as a real bank with the same rules applied as to other normal banks where you can step into the office.

Maybe if you buy models to be used inside commercial games. I would think about first setup a contract with the company before making the payment. Otherwise in the case of some legal problems you have Paypal in the middle. Also with Paypal if you buy something, then most of the time it's not really clear from the invoice what you have bought. In the case you need this as some sort of proof.