If he's giving you cash, there is no way I'd make him sign a bill of sale. Even if he tried to take you to small claims court, he would have to prove you made a promise you didn't keep. I have no idea how he'd do that. With check or PayPal, he can reverse the transaction, then it's you suing him and that's not a fun situation to be in.

However, I have taken non refundable deposits on games to be picked up at a later date. In that case, yes, I have either written or signed something every time. Both that I received money, and needed to be paid in full by a certain date.

I'd sell to anyone with cash, I'd only take PayPal from people with a very very good reputation.

If you've never sold a game to someone who has done something stupid by not knowing what they were doing in the first 30 days, consider yourself lucky.

I always help out, these are old machines and moving them is stressful. But there is no way I'm putting it in writing. I can be a stand up guy without a contract, but if they performed some amateur surgery on something that didn't need it, I don't need to be on the hook for that.