Project Alpha

From Wikipedia:

Project Alpha was a hoax orchestrated by magician and skeptic James Randi. It involved the “planting” of two fake psychics, Steve Shaw and Michael Edwards, into a paranormal research project. The researchers became convinced that the pair’s psychic powers were real. The hoax was later revealed publicly, leading to a backlash against the entire paranormal field.

The success of Project Alpha led Randi to use variations of the technique on several other occasions. Perhaps the most famous example led to the downfall of TV evangelist and faith healer Peter Popoff, when Randi had a male postman pose as a woman with uterine cancer, which Popoff happily “cured”. In another example, Randi hired a performance artist to pose as a channeller known as “Carlos”, who was presented on Australian television and soon had a wide following. After this hoax was exposed the artist was constantly approached by people who believed him to be “real”, even if he told them directly that he was an actor.

(via reddit)