I just saw Eight Men Out which details how some members of the 1919 Chicago White Sox team took bribes and intentionally lost the World Series. While some may have been innocent and others may have been forced to go through with the plan, it is clear that this is one of sports most notorious crimes.
Yet, it is evident that the Series could have been thrown in a much more subtle way both then and today. There's no need to get so many people involved. There's no need to make so many bad plays.
Most games turn on one or two plays. On those plays, there are generally more than one crucial person. With the amount of money that is available for a "clean fix" I think it is probable that many games have been secretly fixed.
It would need to be done without "moving the line" so people/authorities wouldn't notice unusual activity.
Think back to this year's playoffs, and how close the games are. Umpire decisions, big hitting situations, tough pitching spots.
I honestly think the right person, 1 person could throw a game and a series.
I'm convinced it happens in the regular season. More so in terms of over/unders, piling on, or letting up.
If the crooks aren't greedy so that they "need" to win every time, but rather will take six or seven out of ten then it is impossible to notice.
An umpire with a really loose strike zone can "even out" the talent difference between a great pitcher and an average one. Just one umpire with a wide strike zone will cause the over/under to tend towards the under.
I say all of this to say, don't think just because there hasn't been any evidence of a blatant scandal in a while that it doesn't happen. With computers and more sophisticated people involved, it is possible it is more evident.