The short answer is yes, it is possible to cheat at blackjack. The long answer is more complicated and depends on a number of factors specific to the game being played.
In general, it’s possible to cheat by counting cards or by using strategy tips that allow you to make more advantageous bets than the rules permit. But there are also a number of ways to cheat that are more subtle, such as altering the cards you deal or pretending to have a different hand than you actually do.
So, while cheating is definitely possible at blackjack, it’s also not an easy task and requires a great deal of skill and subterfuge. As a result, most casinos frown upon cheating and punish players who are caught engaging in it.