A Massachusetts purchase agreement is the standard legal form for selling or purchasing a home. It documents the transaction's stipulations.A Massachusetts residential purchase agreement is a legal document that secures a real estate transaction between a buyer and a seller. Parties: the "SELLER," agrees to sell and. , the "BUYER," agrees to buy, the premises described in paragraph 2 on the terms set forth below. The sample forms here are for reference and educational purposes only. This file contains detailed instructions for completing the NWMLS Form No. 21, a Residential Real Estate Purchase and Sale Agreement.