More than half of them are fixed. If a trainer tells the jockey to hold back a key horse that has a chance to win if allowed to run, that's fixing. It doesn't matter who else wins.
At small harness tracks, every race is fixed that way. Arabians----every single race is fixed except the biggest stakes. At thoroughbreds, the small tracks are terrible. Fixing in 70% of the races. That doesn't mean they know who will WIN. It means they know who will LOSE at a short price. Big edge in the exotics. The worst are Charlestown and Mountaineer, then Penn and the Ohio Tracks, then the Massachusetts and Louisiana tracks, but almost any track with a base purse under 10,000.
The most profitable trick is the chalk-bomb exotics The even money runs like it should, but the next two or three short prices are all held back. Throw out a couple more that aren't fit, and you have a 5 horse wheel. The favorite almost always wins because its competition isn't trying. The next three are all over 10-1. The exacta will be $40 for $10, the Tri $200 for $40, the super $1,500 for $120. Good money for a $4.00 horse. It happens two or three times a week at the little tracks.