Online sports betting companies enlist celebrities, offer free bets and dole out perks to promote a tantalizing possibility: winning.

But some gamblers who manage to beat sportsbooks say they are often shut down when they succeed too much.

Dave Holmes, a sports bettor in Chicago, said that as he started to win more using a math-based wagering strategy, companies including BetMGM, ESPN Bet and Caesars began rejecting his bets. He typically puts down about $100 per bet. Some companies have offered instead to accept as little as 50 cents.

“I would love to actually be given an answer to why it’s happening, and they refuse to do that,” Holmes said.

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