A shill, also called a plant or a stooge, is a person who publicly helps or gives credibility to a person or organization without disclosing that they have a close relationship with the person or organization. Shills can carry out their operations in the areas of media, journalism, marketing or other business areas. A shill may also act to discredit opponents or critics of the person or organization in which they have a vested interest through character assassination or other means.

Shill typically refers to someone who purposely gives onlookers the impression that they are an enthusiastic independent customer of a seller (or marketer of ideas) for whom they are secretly working. The person or group who 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 professional marketing campaigns. Plant and stooge more commonly refer to any person who is secretly in league with another person or organization while pretending to be neutral or actually a part of the organization he is planted in, such as a magician's audience, a political party, or an intelligence organization (see double agent).[citation needed]

Shilling is illegal in many circumstances and in many jurisdictions[1] because of the potential for fraud and damage; however, if a shill does not place uninformed parties at a risk of loss, but merely generates "buzz," the shill's actions may be legal. For example, a person planted in an audience to laugh and applaud when desired (see claque), or to participate in on-stage activities as a "random member of the audience," is a type of legal shill.[citation needed] Shill can also be used pejoratively to describe a critic who appears either all-too-eager to heap glowing praise upon mediocre offerings, or who acts as an apologist for glaring flaws.[citation needed]