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 agree with you. It is wrong because the casinos think you are trying to play smart. And by smart, it means make more profits from your bet than necessary. They'll be thinking to themselves, they should be the one making more profits off of our bets and not you, the gambler. How they know about gamblers who do it is still something I am yet to figure out myself but they just know.