For example, a "buyer" is a person who purchases finished goods, typically for resale, for a firm, government, or organization. (A person who purchases material used to make goods is sometimes called a purchasing agent.) In product management, the buyer is the entity that decides to obtain the product.
On the other hand, sales representatives sell retail products, goods and services to customers. Sales representatives work with customers to find what they want, create solutions and ensure a smooth sales process. Sales representatives will work to find new salesleads, through business directories, client referrals, etc.