In our sport a cheater is someone who breaks the rules INTENTIONALLY to gain a competitive advantage. Be very careful tossing that accusation around. If you didn't personally witness it then you are not the person who should make the claim. Even if you saw something you should talk to the person involved before taking it anywhere else. We are all human and make mistakes. A mistake is not cheating as it is not done on purpose.
We all break the rules, sometimes without realizing it, sometimes on purpose. Every footfault is a violation. Almost none of them get called. Unless you purposely footfault to get an easier shot it's not cheating (in my book anyway). It is common to break non-competitive rules (where there is no advantage in terms of scoring): Flipping a disc rather than using a mini, picking up gimmes rather than making the player putt out, shooting out of order, throwing a disc with a store price tag sticker on it, etc. None of these are cheating either, IMO.
Disc golf is a sport where an ethical code exists. We police ourselves. Referees don't watch our shots and call violations. This creates a spirit of the game unlike most other sports and the title of "cheater" can stick for a long time, fair or not. For players new to the game, who don't yet understand the culture, gentle latitude should be given.
For all the concern of cheating, in the Pro ranks it is very rare. Those who are shaky in this regard are known and watched carefully. Most situations which arise involve rules/interpretations where the facts are fuzzy: was it OB?, where did it go OB? can you move that branch? can you stand on top of the picnic table to make the shot? Is that casual water?
Cheating at an Ace Race? That's a new one. Aside from overt collusion, how do you cheat? The old joke: What score does the cheater claim when he hits a hole in one?