By signing this contract, I choose to purchase the motor vehicle on credit according to the terms of this contract. My bank wants purchase agreement or bill of sale before sending out a check to the dealer.In this guide on how to buy a car in Texas, you'll learn what documents you need, how to get financing, and more for new or used cars. The retail installment contracts in the list below have been accepted as plain language contracts under the provisions of the Texas Finance Code. One contract is the car purchase or sales agreement where you contract with the dealer to purchase the vehicle. A Texas Vehicle Purchase Agreement is a legally binding document that outlines the terms and conditions of a vehicle sale in Texas. You'll need to sign the car purchase agreement (or dealer bill of sale), the title, an odometer statement, and sometimes a damage disclosure statement. Vehicle Payment Plan Agreement. A vehicle payment plan agreement is a contract between a buyer and seller of a vehicle that agrees to installment payments.