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As far as I know, the only working way (at least from the bookmaker's side) is to look at the volume of bets. If the volume is sharply higher than the average for a regular match (we exclude top events), then such a match is often considered suspicious and bets are returned to all those who have already made them.
Have you came across that scenario where the bets you made were voided. I got bets getting voided but usually those are issues with the bookmaker and not because of manipulation and leaked outcomes. Even if there is corruption in sport you wont be knowing about it until years when there is an investigation that exposes them and by that time nothing changes in the bets you made.
I have had some bets voided but it is not because of the bookmaker but because of the game itself.
Anyway, corruption is everywhere and sports is not excluded in this human behavior.