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.