Giving a real estate agent the "exclusive right to sell" your property does not mean that there will not be other agents involved. Your agent is the listing agent and part of his or her job is to market your home to other agents who work with buyers. Those agents will show your home to their clients. Regardless of who sells the home, even if you sell it yourself to a friend at work, your listing agent will earn a commission.
An exclusive right to sell is the only type of listing an effective real estate agent will accept. This is because they have a reasonable expectation of earning back any money they spend on promoting and marketing your property.