A bill of sale shows that a transaction took place on a specific date, proving that both parties wanted a transfer of ownership. When a vehicle owned by an estate is sold to a third party, a bill of sale (signed by the estate executor or disposer) is required, in addition to the other documents listed here. You need a bill of sale. As the official receipt of a private used car sale, a bill of sale is used to transfer ownership of a used vehicle from the seller to the buyer and is required by most provinces to officially register the car under the new owner's name and license plates. You can write your own bill of sale, or.