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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.