A shill is an associate of a person selling goods or services or a political group, who pretends no association to the seller/group and assumes the air of an enthusiastic customer. The intention of the shill is, using crowd psychology, to encourage others unaware of the set-up to purchase said goods or services or support the political group's ideological claims. Shills are often employed by confidence artists. In the UK the term plant is also used.
Shilling is illegal in many circumstances and in many jurisdictions because of the frequently fraudulent and damaging character of their actions. 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 appropriate (see "claque"), or to participate in on-stage activities as a "random member of the audience", is a type of legal shill.
"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. In this sense, they would be an implicit "shill" for the industry at large, as their income is tied to its prosperity.
Both the illegal and legal gambling industries often use shills to make winning at games appear more likely than it actually is. For example, illegal Three-card Monte peddlers are notorious employers of shills. These shills also often aid in cheating, disrupting the game if the "mark" is likely to win.
In a legal casino, however, a shill is sometimes a gambler who plays using the casino's money in order to keep games (especially poker) going when there are not enough players. (This is different from a "proposition player" who is paid a salary by the casino for the same purpose, but bets with their own money.)
In online discussion media, satisfied consumers or "innocent" parties may express specific opinions in order to further the interests of an organization in which they have an interest, such as a commercial vendor or special-interest group. Websites may also be set up for the same purpose. For example, an employee of a company that produces a specific product may praise the product anonymously in a discussion forum or group in order to generate interest in that product, service or group. In addition, some shills use sock puppetry where they sign on as one user soliciting recommendations for a specific product or service. They then sign on as a different user pretending to be a satisfied customer of a specific company.
In some jurisdictions and circumstances this type of activity may be illegal. In addition, reputable organizations may prohibit their employees and other interested parties (contractors, agents, etc.) from participating in public forums or discussion groups in which a conflict of interest might arise, or will at least insist that their employees and agents refrain from participating in any way that might create a conflict of interest.
In marketing, shills are often employed to assume the air of satisfied customers and give testimonials to the merits of a given product. This type of shilling is illegal in some jurisdictions but almost impossible to detect. It may be considered a form of unjust enrichment or unfair competition, as in California's Business & Professions Code § 17200, which prohibits "unfair or fraudulent business act[s] or practice[s] and unfair, deceptive, untrue or misleading advertising".
Shills, or "potted plants", are sometimes employed in auctions. Driving prices up with phony bids, they seek to provoke a bidding war among other participants. Often they are told by the seller precisely how high to bid, as the seller actually pays the price (to himself, of course) if the item does not sell, losing only the auction fees.
Shilling has a substantially higher rate of occurrence in online auctions, where any user with multiple accounts (and IP addresses) can shill without aid of participants. Many online auction sites employ sophisticated (and usually secret) methods to detect collusion, and a number of people have been sent to jail for online auction fraud in the past decade.
Shill bidding may be a common practice on eBay. In his book "Fake: Forgery, Lies, & eBay" Kenneth Walton describes how he and his cohorts placed shill bids on hundreds of eBay auctions over the course of a year. While many sellers consider shill bidding a harmless act, some believe that it may violate federal or state laws. Walton and his associates were charged and convicted of fraud by the United States Attorney for their eBay shill bidding. Some eBay sellers frown on the practice and a few spend considerable time trying to "out" those among them who use shill bidders as well as working to increase public knowledge of how to protect themselves from said shilling. Their tactics can easily turn up many "false positives" — for instance, they believe that auctions having many bidders with very low (less than 20 or so) and/or no feedback could be suspect.
The term is applied metaphorically to journalists or commentators who have vested interests in or associations with parties in a controversial issue. Usually this takes the form of a show or network pretending to be offering news when in fact they are simply repeating talking points offered by a political party.
In addition, there have been some notorious news conferences, such as the U.S. Federal Emergency Management Agency conference in which agency staffers posed as news reporters. Shill reporters have also been used in White House briefings.
Plants can be used by police or military interrogators to aid interrogation. The plant can pose as a fellow inmate or internee and build a rapport and earns the confidence of the interviewee. The plant may subtly suggest that telling the interrogators what they want to know is the sensible or right thing to do. Even if no outright confessions are obtained, minor details and discrepancies that come out in supposedly innocent conversation can be used to chip away at the interviewee. Some plants are in reality inmates or prisoners of war who have been promised better treatment and conditions in return for helping with the interrogation.
One notorious UK case is that of Colin Stagg, accused of the murder of Rachel Nickell, in which a policewoman posed as a potential love interest to try to tempt Stagg to implicate himself.