Blackjack dealers are human just like the rest of us. While they have been trained and have practice in dealing the cards and making payouts, every now and then a mistake happens and the payout is incorrect.
By incorrect I mean that perhaps a player is paid for a push. Or the player might have lost and be paid anyway. Or the incorrect amount for a blackjack or win might be paid.
When such a thing happens novice players wonder what they should do about it and whether or not it is legal in the game.
First off, if you receive a payout that is more money than you are supposed to receive or receive one when you are not supposed to be paid it is not illegal in the casino. It is not considered cheating in blackjack. This is a mistake on the dealer