Even if you are cheating, and they know you're cheating, they might leave you alone if you're not that good at cheating. Take card counting: While counting cards in one's head is not illegal, a good card-counter in blackjack gains a statistical advantage over the house, and if the casino decides the counter is making too much money, he or she will be escorted off the premises.
But card counters have to be really good: One mistake an hour could swing the advantage back to the house. And casinos don't mind that. "If you're not perfect at card counting, you can still lose money," Jonas said. "They'll watch you count cards and if you make any mistake they'll just let you play."