Never sign a contract with spaces left blank, mark them out or fill them in as appropriate. 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. Are you looking for a loan agreement form in Washington? Download our free Washington Loan Agreement Form which is available as PDF or Word documents. Sufficient income, credit and a history of paying debts on time are among the top criteria lenders seek in an applicant. Use our free payment plan agreement form to spell out all the terms and conditions of a loan if you need to establish a payment schedule with someone. When you buy a car at the dealership, you'll need to sign the car purchase or sale agreement along with other documents. Find out what you'll sign and why. You're ready to get your first car loan but aren't sure where to start.