An Arizona residential purchase agreement is a legal document outlining the terms and conditions for a buyer's purchase of residential property from a seller. A payment plan agreement outlines an installment plan to repay an outstanding balance over a specified time frame.Customize and Download this "Sample Land Purchase Agreement". The Buyer agrees to pay. An installment purchase agreement is a contract where a seller will let a buyer incrementally pay for a property or asset. This attachment should be given to the Buyer prior to the submission of any offer and is not part of the Residential Resale Real Estate Purchase.