San Diego County Credit Union offers new and used auto loans to get you in the vehicle of your dreams. I'm going to show you stepbystep how to walk through and fill out the California residential purchase agreement or the RPA.CAR (California Association of Realtors) residential purchase and sale agreements are widely used in real estate transactions throughout California. A vehicle purchase agreement represents the document that lists the legal obligations of both the buyer and seller. Check box 3G(3) on the Residential Purchase Agreement (C. A.R. Form RPA) and attach the form Seller Payment to Buyer's Broker (C. The Finance team at Karz Plus is happy to help you. I'm new to car financing. What got me confused is that my bank wants purchase agreement or bill of sale before sending out a check to the dealer.