Find out what documents you will need to provide proof of sale and ownership if you are buying, selling, or gifting a vehicle. You can prepare an Agreement for a Joint Purchase using the form included here.Simply fill in the details of your joint purchase. 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. Watch this before you finance your next car (former dealer explains how to read a purchase contract) The final hurdle you face is signing the vehicle purchase agreement; a confusing and convoluted document that we explain in detail here. We are the preferred dealer in Brooklyn, NY. Get a quote on any of the new or used vehicles from our vast inventory. This form certifies the purchase price and determines the sales tax you must pay when registering the vehicle. If you're leasing a vehicle, most finance companies will include a buyout option as part of your lease agreement.