shill

A shill, plant or stooge is a person who helps a person or organization without disclosing that he or she has a close relationship with that person or organization. Shill typically refers to someone who purposely gives onlookers the impression that he or she is an enthusiastic independent customer of a seller (or marketer of ideas) that he or she is secretly working for. The person or group that hires the shill is using crowd psychology, to encourage other onlookers or audience members to purchase the goods or services (or accept the ideas being marketed). Shills are often employed by confidence artists.