Payment : The bill of sale document should also state the method of payment used such as installments or in full, cash, check, credit card or bank deposit. The California bill of sale form helps individuals document data on a transaction involving the sale, trade, or gift of personal property.The dealer must provide a written document with the price of specified items purchased and their effect on installment payments (California Civil Code §2982). A bill of sale for a trailer is an essential document that provides proof of ownership and outlines the terms of the sale. You need a bill of sale in California if you're buying or selling a horse or, in many cases, if you register a car that you bought from a private seller. A bill of sale will detail a transfer of property or sale of items between a seller and buyer. This type of document serves as legal evidence. In many cases, yes, a bill of sale can be used as a contract depending on the circumstances. However, there could be other elements that are also required.