Charlie Miller, Max Malini, Dai Vernon/"The Professor", Larry Jennings, Nate Leipzig and Jacob Daley are all famous sleight-of-hand magicians. In fact, nearly every major male character in the film is named for a sleight-of-hand magician.
The hands seen performing card tricks in the beginning of the film belong to writer/director Damian Nieman (who's hand wears a spade ring), R. Paul Wilson, Jason England, and Earl Nelson, all real life card mechanics. Nieman also taught (along with Earl Nelson and R. Paul Wilson) Sylvester Stallone and Stuart Townsend how to perform their card tricks for the film.
Bo Hopkins' character is named John Scarne. John Scarne was also a famous sleight of hand artist during the mid-20th Century. He was best known for exposing crooked gambling to the public. In The Sting (1973) he doubles for Paul Newman's hands.
In the beginning of the movie, you see a lot of card cheating devices that have been used throughout the 19th and 20th Century. Among them is the Kepplinger holdout device which was the most popular card cheating device used.
Throughout the movie you see Sylvester Stallone's character putting a special oil on his hands from time to time. This is done by many card magicians (not just cardsharps) to keep the hands soft so that you can manipulate the cards easier.
All of the playing cards used are manufactured by the United States Playing Card Company. The brands shown are Aristocrat (very hard to come by), Bee, Bicycle, and Tally-Ho (which is primarily available in the New York City/Long Island area). The USPC also created special decks of casino grade Aristocrat SHADE cards with the film logo as a gift to writer/director Damian Nieman.
The book shown throughout the movie, "The Expert at the Card Table" by S.W. Erdnase, is known as the "Cardman's Bible". Originally published in 1902 for cheating purposes, it is still considered the best book on card manipulation. It is a quote of Erdnase which is shown onscreen as the film begins.
Many situations in the movie are references to the book on Dai Vernon by Karl Johnson, "The Magician and the Cardsharp". For example, Malini gets his name from a famous magician referred to in the book; and "shade" is defined as a cardsharp's cover move, as it is in the film.
The Director "Damian Nieman" is also a professional card magician, and required the cast to perform their own magic tricks. The "making of" documentary that comes with the DVD is worth the view, just for the amazing tricks.