In a buyer-seller relationship, reciprocity refers to the practice whereby a seller requires the purchaser of one product to buy another item in the line. an industrial buying practice in which two organizations, in this case a manufacturer and a supplier, agree to purchase each other's products and services. an arrangement a manufacturer makes with a reseller to only handle its products and not those of competitors. the illegal practice of refusing to purchase a seller's products unless the seller agrees not to purchase that product or any similar products from any other buyer. when a supplier requires a buyer purchasing some of its products to also buy others.