A casino can legally refuse to pay out a blackjack win under certain circumstances, such as if they suspect cheating, identify a mistake or error in the game, or if a player violates the casino's rules. Additionally, disputes over how a hand was played may lead to withheld payouts until the issue is resolved. However, as long as you're following the rules and no errors or misconduct occur, most casinos will honor your winnings. If a refusal happens unjustly, you may challenge it through the casino's management or a local gaming authority.