yeah, it happens. For example, in my local Rotax races there are obvious cases of drivers who are cheating with the engine, but because the inspectors only check the external parts nothing happens to them
I race dirt oval in East TN with my son. He is a beginner in Predator, box stock, fixed gear-18/65, and 4k rpm. He has done well with some 1st, 2nd, and 3rd place finishes this year. But lately, he has been competing with folks who end up over half a track ahead of the pack at the finish. One of his competitors outweighs him by 90 pounds on the scale. So, I suspect there must be a reason for the obvious advantage. My point is, that some folks will do just what it takes to win.