Parties: the "SELLER," agrees to sell and. , the "BUYER," agrees to buy, the premises described in paragraph 2 on the terms set forth below.A Massachusetts purchase agreement is the standard legal form for selling or purchasing a home. It documents the transaction's stipulations. Purchase and Sale Agreement. A purchase and sale agreement is a contract between a buyer and seller for transacting a property in exchange for a specific price. This file contains detailed instructions for completing the NWMLS Form No. 21, a Residential Real Estate Purchase and Sale Agreement. This form can be used to add or remove a buyer or seller's name, or correct an error, or revise a term of the agreement.