Price discrimination
Johnson insisted the casinos have only themselves to blame for their losses, opening the door by offering him high-stakes gambling. They also agreed to discount 20 percent of his blackjack losses as an incentive to get him to play, he said. For instance, if he lost $1 million, the casinos would forgive $200,000.
He ended up winning $15 million. The article is interesting throughout, and hat tip goes to Steve Silberman, more on the math here from Kid Dynamite.