Casino cheating is as old as casinos themselves. Cheating methods can be very complex (using electronics to keep track of card position during a shuffle) or crude (the old "snatch and grab" of chips from a gaming table) but they'll probably always be around.
Any time you have a lot of money exchanging hands for a game, there are going to be attempts to cheat. Even highly-organized games like professional football and baseball have had their cheating scandals. Casino blackjack is no different--blackjack is already one of the "friendliest" games in the casino, so attempts to cheat that edge just a little bit more toward the player are nothing new. Since a player using perfect blackjack strategy is only at a 0.5% disadvantage, gaining even a slight edge can turn blackjack into a positive expectation game, which may explain why so many blackjack cheats have been attempted.
All of the cheating methods discussed here are illegal and will get you arrested. No one cheats a casino for long, if they even have the opportunity to cheat them out of any money at all.
The earliest forms of blackjack cheating are still in practice today. The simplest form of blackjack cheating is known as "dealer collusion," a fancy word that just means making friends with a blackjack dealer who helps you win and splits the prize with you. Blackjack dealers know how to get away with a blown game here and there, and can signal you to bet a certain way at a certain time, and since the blackjack cheat assumes the dealer can "get away with it," he has no problem colluding with the dealer. Unfortunately for the wannabe blackjack cheat, today's casinos have so many eyes on their tables that dealer collusion is just asking for trouble.
"Spooking" is another old blackjack cheat that some people still attempt. For this cheat, the "spook" sits behind the dealer and attempts to surreptitiously peek at the dealer's hole card when the dealer looks at it. He then signals his partner at the table what the card is or how to bet. Like dealer collusion, in spooking, the spook and the cheater split the cash.This is highly illegal and is easy for casino security to catch.
Making a tiny mark, scratch, or spot on a particular card or set of cards is called "marking" and is another cheat from the earliest days of casino blackjack. Women blackjack cheats are notorious markers--their long nails and makeup make it really easy to mark cards and claim ignorance at a later date. Markers tend to put marks on aces and face cards, even using these marks to inform legal blackjack tactics like counting and shuffle tracking. The big downside to marking cards is that if a mark is small enough to get past the dealer, it is probably too small to see from a distance.
Mucking and Switching
The final old school blackjack cheating method is called "mucking" or "switching." With these methods, you replace cards in your hand with other more advantageous cards. Muckers take cards from the dealer's deck, while switchers bring their own cards in their pockets or up their sleeves. This is obviously illegal, and unless the mucker or switcher has top-notch sleight of hand skills, it is easy to catch.
Using electronic devices or small computers, modern blackjack cheats have brought cheating the casino into the 21st century. Though these machines are sold as "card counting" aids, using them in the casino is still illegal, even though card counting itself is not against the law. These machines keep track of cards and card counts, and can even help in more complex counts like shuffle tracking and analysis. These devices are usually pocket-sized and rather plain-looking to hide what they actually--electronic blackjack cheats.
The use of wireless communication systems for cheating at blackjack in the casino has been attempted, but casinos monitor for this kind of communication, with some casinos even jamming or blocking certain frequencies to prevent people from communicating wirelessly. The idea behind wireless communication is to signal players without having to make an obvious "signal" like scratching your nose or some other giveaway. Since many casinos block out the ability to use wireless devices for communication, cheaters who want to talk to each other without using physical signals will have to build a better mousetrap.