Three-card monte is a classic con. The dealer allows the 'mark' to think that he has outwitted the dealer. In this demonstration, Shermer shows exactly when the con is pulled and the psychology of why it's almost impossible to beat.
Sometimes the con will involve shills, people who pose as audience members but are in fact, in on the con. The end to a classic con often comes with the mention of the police being seen, the ultimate threat to any legitimate gambling scheme.