Cheating is basically intent and there are three judges on that intent: You're own, your competitors, and the sanctioning body.
I'm a national level scrutineer for SCCA road racing and we catch people all the time not meeting the rules. The vast majority of these folks are not cheaters, they've made a mistake. Last weekend at the double regional at Buttonwillow there were two perfect examples of cheating and just making a mistake.
After the qualifying session for the open wheel cars one of the Formula Mazda's came across the scales 11 lbs. underweight. The driver and crew chief both admitted that they made a mistake and under fueled the car for the session and accepted their grid position at the back of the field with grace. No one in Tech thought these guys were cheaters, they just made a mistake.
A Formula Ford driver had 6 water bottles in his lap as he came up to the scales and was chugging down the 7th as fast as he could. I asked him to hand me the water bottles in his lap and he said no, he was overheated and needed to cool down. His wife and crew chief both agreed and said he was in danger of heat stroke. I said I'll radio for the ambulance. All three said, "No." I then asked again for the water bottles and they handed them over. That car scaled in 8 lbs. underweight. At that point their arguments began - "Unfair", "He's the fastest anyway and should start up front", "Its just a regional race so why are the car being weighed", "Your scales are wrong", "Its only 8 lbs." Those folks were cheaters.