Arbitrage betting is forbiden on casinos, they consider it as an abuse, and I don’t know how but they will know if you are doing it with multiple casinos, so, users must be careful about this linda of practices because just as op mention they will close your account and keep your money of you they it.
I think that's the purpose of KYC verifications, your account can be linked and traced if seen on different betting platforms...But thinking about I would say it's still puzzling to know how they end up fishing out bettors use this system of betting, the only logical explanation is if the bookmakers are sharing informations of their users with other bookmakers just to monitor suspetious activities, otherwise I can't rely figure out how