selling agreements are detailed contracts that outline the terms associated with a sale of goods or services to a third party. they are normally used when goods, services, or items are sold and need to be delivered to the customer. when you create a selling agreement, it is important to describe the product or service you are selling in as much detail as possible. there are two parties involved in a selling agreement: the buyer is the person or company that is purchasing a product or service from the seller. this may be any of the following: sales and purchase agreements are a specific kind of sales agreement that can be found in a number of business scenarios.