The property and improvements which the Seller is agreeing to sell and which the Purchaser is agreeing to purchase is known as. A purchase and sale agreement is a contract between a buyer and seller for transacting a property in exchange for a specific price.This is a Legally Binding Contract; If Not Understood, Seek Competent Legal Advice. An Alabama residential purchase agreement allows a buyer and seller to enter into a legally binding contract for the sale of real property.