The issue with card counting in blackjack is that to have an advantage, the player must vary their bet size according to the count. Casino surveillance personnel and floormen also know how to count cards, and when they see the player raise and lower their bet consistently with the count, will do one of three things. First, they will "flat-bet" them - tell them that they are welcome to play, but must bet the same amount from the beginning to the end of each shuffle. If the player is caught a second time, they will be told that they are welcome to play any game in that casino except for blackjack. On strike 3, they will be "trespassed" - walked off the property by casino security, and told that if they come back, the police will be called and they will be arrested. Some casinos skip directly to step 3, especially if they suspect team play (where a player is betting the minimum while counting, and signals for a big player to come in and bet the max when the count is favorable).
