Don't do business buying or selling an appliance, even if it is only once, without proper paperwork to back up the sale.
If you buy from a private party or sell as a private party, be prepared with a receipt form.
Use the one that you can
download and print here.
A customer will feel much better about the deal if he/she has the receipt as an Appliance Bill Of Sale in hand.
The buyer paid, and will feel better when he/she knows that a bill of sale is proof against any claim or to prove that it is the same item that was sold.
A buyer will feel better about doing business with you next time.