Compulsive gambling is driven by the hope of winning a large amount, so one way to deter gambling addiction is to forbid paying out winnings to people registered as having this problem. In a one-shot interaction, casinos and lottery organisers clearly have an incentive to keep both the stakes and the winnings, but problem gambling is repeated. Sufficiently patient casinos are motivated to establish a reputation for paying out winnings, if the punishment is small or unlikely enough, because such reputation attracts other gamblers, which increases the long-run expected profit of the casino. The gamblers are not interested in reporting the casino for illegally paying out, because they benefit from the payout, and the closure of the establishment would prevent them from satisfying their craving.
However, the gamblers’ desire for big winnings, even with very low probability, can be used to motivate them to report – the law can offer a large sum to anyone who proves that a casino made an illegal payout. The reward can be financed from an even larger fine levied on the law-breaking casino. The reward should of course be in addition to any winnings of the whistleblower if the latter is a patron of the casino, because a gambler should not lose money by reporting. Gamblers are impatient, unlike casinos, so the repeated interaction with an establishment does not outweigh an immediate payout, even if collecting the payout leads to less opportunity to gamble in the future.