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I don't see any need for such big and serious leagues to rig the game, because they get a lot of money from advertising anyway. Why would they risk their authority and persuade several unreliable people to collude?
Only small leagues that don't get such huge amounts of money and their teams (or individual players) are forced to look for additional sources of income need this. In general, my opinion is that they hardly do this.
That's right, I agree with you, it's very difficult to fix matches in major leagues, even if it's done long before the season starts. We know that match fixing ever happened in football historically, such as in Serie A involving Juventus, and even in the Champions League involving Marseille. But nowadays, we never hear of such things happening again, and players and referees found involved will face severe sanctions when doing it.
Lastly I only heard about Sandro Tonali when he played for AC Milan and Nicolo Fagioli of Juventus, betting on the matches they played, and they got a ban for almost a season.