A Washington purchase agreement documents the sale of a piece of real property for a specified financial figure. A purchase and sale agreement is a contract between a buyer and seller for transacting a property in exchange for a specific price.Download a Washington residential purchase agreement template to streamline your real estate transaction and clarify relevant details. A Washington residential purchase agreement is used when making an offer to purchase real estate. The agreement initiates the negotiation process. The Washington residential purchase and sale agreement is a legally binding contract between the seller of residential property and a buyer. This FSBO paperwork is needed as soon as you accept an offer, so it's useful to have a purchase agreement onhand that you can fill out quickly. Free Real Estate Purchase Agreement. Answer a few simple questions.