Contract involving transfer of the possession and ownership (title) of a good or property, or the entitlement to a service, in exchange for money or value is known as a sale .Essential elements that must be present in a valid sale are:
(1) competence of both the buyer and seller to enter into a contract,
(2) mutual agreement on the terms of exchange,
(3) a thing capable of being transferred, and
(4) a consideration in money (or its equivalent) paid or promised.