County of Harris. §. By signing this contract, I choose to purchase the motor vehicle on credit according to the terms of this contract.Before you drive off the lot, be sure to have a copy of the contract and all other documents that you and the dealer have signed. First you must choose between buying a new car and buying a used car. Obtain a Bill of Sale: Both parties must fill out and sign the Bill of Sale as part of the transaction. The article includes information about warranties, vehicle title searches, auto insurance, financing, canceling a purchase, and the Texas Lemon Law. Information you can expect to fill out includes the car's VIN, make, and model, the name and permanent address of each party involved, and the sales amount.