I wouldn't accept Paypal and I would not include a description of the machine (other than that it is "used") that could be interpreted/enforced as a (mis)respresentation even though no warranty is offered. Keep it simple -- less is better: bill of sale listing machine with serial number and any other items you include. I would also state: sale is final, no refunds, no returns, item is sold to and accepted by buyer as is in used condition with no warranties express or implied. Sign and date.

However, it appears that you need to have a conversation with the buyer. It sounds like he wants to be covered whereas you do not want to cover after the sale. These basic terms should be agreed to verbally before you move forward.