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What have your experiences about this been? Is match fixing considered a common occurrence in leagues you place bets at?
No experience so far or at least not to my knowledge. I also prefer betting on top leagues like most members. I have heard of match fixing accusations from local sport leagues but it's usually the accuser's words against the accused. No real evidence to support it so I cannot really call the game as rigged. There are bettors that are just sore losers so can't take them seriously.
You're right, any reputable gambling sport should not engage on match fixing in other for them to gain their spectators trust, those that do this at the local level may not be that observant about it to that extent by knowing if the people really want that or not, but i see no gain in fixing a match than where manipulations is an order of the day, people may not want to for such sports to gamble because they know that it's been fixed by the organizers.
It is not about the reputation of a specific sport. I think most sports really have a good reputation in general, but when you have got some people who want to take advantage of an offer from the mafia or something, it can be bad for the sport of course.
I remember that Djokovic said he was approached a couple of times with high offers to fix some tennis matches. That is actually one reason why I think players or sports professionals should earn enough to get well along because that makes them less prone to saying yes to illegal stuff like that.
But there is also force from these organizations that try to bribe referees or players. Imagine players or referees get threatened by some dangerous people. There isn't much they can do against it.