This document becomes important when you need to buy or sell personal property. You may associate bills of sale with used vehicles, but you can use this document for a variety of items.Ī bill of sale will detail a transfer of property or sale of items between a seller and buyer. A bill of sale, proof of purchase, proof of payment, As Is Bill of Sale, Proof of Sale, Sales Slip, or Sales Receipt, is a document or receipt used to transfer the ownership of an object such as a vehicle.