Bonuses
Many online casinos offer sign-up bonuses to new players making their first deposit, and often on subsequent play as well. These bonuses are a form of marketing that may incur a cost (potentially justifiable in order to attract a new player who may return and deposit many more times), since the casino is essentially giving away money, in return for a commitment from the player to wager a certain minimum amount, usually a multiple of the deposit and/or bonus credited to the player's account. Since all casino games have a house edge, the wagering requirements ensure that the player cannot simply walk away with the casino's money, and indeed if the wagering requirements are sufficiently high, he may in fact have a negative expectation, exactly as if he had deposited without any bonus.
Casinos may choose to restrict certain games from fulfilling the wagering requirements, either to restrict players from playing low-edge games, or to restrict 'risk-free' play (betting for instance both red and black on roulette, thereby completing the wagering requirement with a guaranteed profit, after the bonus is taken into account.
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