or even some other times if it's possible to make money by betting on the two sides of a game
is it?
Dont do this because this is an arbitrage trading and some casino doesnt allow it since you are taking advantage on the odds of the sportsbook. Many syndicate is doing this and earning huge amount of money but they are being monitored already after they make the profit. You might be accused that you are involved on this shady activities and your account might be banned permanently.
Casino preferred to bet only on one side instead of doing arbitrage bet on the two sides of the game. Im not sure if Duelbits allows it but some casino dont condone arbitrage.
This is even rare if 2 casinos are using the same sportsbook and a guy got rate limited on 1 of the casino and got accused on the 2nd casino of unfair gambling techniques.
Arbitrage techniques are more common these days and are hard to detect if the person uses 2 devices with different IP addresses.
Bookmaker is not just basing on IP but rather on the bet pattern of all the user that use there sportsbook. Its easy to spot those cheating with arbitrage trading since they are only doing same bet to the other account. Bookmaker also observe those user who wins the most and this there basis to start the investigation for possible connections of this account.
You can check reputation/scam accusation board and look for thread about casino. Most of the complaints are from user do this kind of illegal activity and using the forum to gain support for there claims.