I have to agree with this especially if the odds provider can't prove the customer has been doing it intentionally (which doesn't seem to be the case here, btw).
It's more of the odds provider's fault than the gambler's fault. Any gambler will try to take advantage of offered wrong bets.

Imo, the best course of action in this case is either to limit the gambler's account or let him withdraw his winnings and tell him that he is no longer welcome to play on their casino. As I said, it's just my opinion.