contracts can be written out, but any buyer who pays for a product or service on the spot automatically agrees to the terms of a sales contract. a sales contract specifies who the parties are, what transaction has taken place, the legal obligations and rights of each party to the contract and information regarding certain contingencies. the contract will specify who exactly each party is. for example, many sales contracts take place between a person, or buyer, and a company, the seller, even though the physical transaction involved a representative of the business. the contract goes on to specify what the nature of the transaction is. then the money would be described in terms of the size of the payment and what form it took — cash, credit or check or any combination.