In my experience fixing is way more common when it comes to district leagues, college leagues and small-cap games. Not the big ones that get broadcasted all over the globe to a huge audience. These small scale games are the bread and butter for many local bookies and fixers. They will make money from them and not do any other job at all - its the primary source of earning among other strongarming jobs.

Hence if you are betting on the big games, dont fuss about fixing much, keep your mind at ease there.