Yes match-fixing has been going on for a long time and even now it still exists in the unpopular minor leagues, this is still a possibility, it's just not highlighted by the media to be reported, so it will be vulnerable if betting on the minor leagues, the bookies can play a role there.
If you don't want to be cheated then bet on big league matches so the bookies won't dare to do this.
Match-Fixing is indeed the best place for bookies to do all the manipulation and manage the match without being suspected because it is very supportive to commit cheating actions that cannot be done in big matches in general.
Minor leagues with clubs and players who have low salaries will be very vulnerable to manipulation,
because players will be easy to bribe with money so that they follow the instructions given by the bookies so that the score is as desired.
Match-fixing is an area controlled by bookies, and they can benefit a lot, because minor leagues also do not get clear regulations and minimal supervision, there is no transparency because the lack of media coverage and public supervision in small leagues creates space for corrupt practices, including match-fixing, so that it goes on without much attention.
For gamblers who like sports matches, it is better to avoid small leagues like this which are prone to being a place of Match-Fixing, it will only benefit the bookie, but if you want to test your luck, pay attention to which team will usually be chosen by the bookmaker.