Shill

A shill is person who is paid to help another person or organization to sell goods or services. The shill pretends to have no association with the seller/group and gives onlookers the impression that he or she is an enthusiastic customer.

With respect to investment and futures web sites that have forums you will frequently find shills promoting trading services by making statements such as "I used this system and made a ton of money" when discussing paid-for trading advisory services. This type of shill is fairly easy to spot because they will be evasive and not answer your questions and will never provide proof of their earnings. The will also not call out their positions ahead of their trades and will only talk about their "winning trades" after they have been completed.

Caveat Emptor.