Seller the following described real estate in. A Washington residential purchase agreement is used when making an offer to purchase real estate.The agreement initiates the negotiation process. A Washington purchase agreement documents the sale of a piece of real property for a specified financial figure. Description of The Property. Upon the terms and conditions set forth herein, Buyer agrees to buy from Seller, and Seller agrees to sell to Buyer, the real property in Yakima, Yakima County,. Ensure you know the legal requirements and disclosures of a Washington real estate purchase agreement. Fill in our template to create your agreement. The Washington residential purchase and sale agreement is a legally binding contract between the seller of residential property and a buyer. Filling out the PSA.