A sales agreement is an important legal document that contains all the agreedupon terms between the buyer and seller for the sale of the property. The Flat Purchaser agrees to purchase from the Builders and the.The property and improvements which the Seller is agreeing to sell and which the Purchaser is agreeing to purchase is known as. A sale deed is a legal document that proves that a property has been transferred from the seller to the buyer. A sale deed refers to the immediate and complete sale of the property. A sale agreement indicates the sale of the property in the future.