When small leagues get caught rigging games, they lose credibility, so do you really think it never happens in major leagues?
Major leagues will not allow this to happen; they are a multi-billion-dollar industry, and they have all the means to catch cheaters and those who offer bribes to fix the games.
We have some players caught engaging in game fixing, but the organisation are quick to ban, charge and fine these players.
Only small players will cooperate in game fixing, as big names protect their livelihood and the reputation they have built over the years.
If the major leagues or organizations fix the games, they would face widespread public scrutiny and likely imprisonment, given the involvement of public interest.