You can prepare an Agreement for a Joint Purchase using the form included here. Simply fill in the details of your joint purchase.1. Enter the names of the Seller and Buyer along with the agreement date. You acknowledge that you have reviewed a vehicle history report for the Vehicle. You also acknowledge that the Vehicle has the following. If you're leasing a vehicle, most finance companies will include a buyout option as part of your lease agreement. 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. A purchase agreement is a type of contract that outlines terms and conditions related to the sale of goods.