In other sports like boxing, tennis, football etc referees can easily influence results too and and sometimes take bribes from betting companies to do this.
What is a foul? Is the serve a fault or on the line? Below the belt hit or not? All opinions.
But fs is much more opinion based so i don't think it would work. What trick is harder, good or bad style, creative or not and everything in freestyle are all about opinions. For fun betting, with no money, would not work either for the same reason.
But it might work in a competition like the 'Pass it on' comp where there is no need for judges and the winner is clear.