By the way, all of this talk about arbitrage betting is pointless because GekkeBelg was top-down betting.
Yes, I mentioned his strategy before, it's called the top down method.
The Top Down Method is when you identify a sharp line from a sportsbook and consider that your “source of truth.” You then pick off advantageous bets at other sportsbooks based on that source of truth.
That's it, there's nothing fancy. No arbitrage betting, no syndicate betting. Just some guy comparing odds.
Do casinos prohibit this strategy? Well, as several users already mentioned here, no. At least not those who had conflict with GekkeBelg. I take a quick stroll on those casinos and can't find value betting on their ToS or sports-rules [I am currently reaching some casinos' representatives to get a better understanding of their view on this, just to be sure] with exception of WinTomato who explicitly describe they prohibit this strategy.
Technically he messed up against BC.Game, because they are freerolling all of their customers
3.3 Sportsbook platform reserves the right to refuse, restrict, cancel or limit any bet. That's why he lost his AskGamblers case against Bc.Game.