A simple authorization letter to sell a car contains the following elements. It states the person or company authorized to sell the car to its verified buyer. The vehicle details, including license plate number, car model, and chassis number, must be accounted for in the authorization letter. Any actions that the authorized person can't perform must be documented, such as selling car parts. The verified buyer's details must also be recorded, including their name, ID, and signature. All receipts and legal documents must be signed along with any additional terms accounted for.