i have rarely seen cheating at a muzzleloader event. I have hear of those trying to "fatten" a hole to make it cross a line or "more than half way in." But I have never seen it. I shot a line shoot last year where I had an AD coming in from 12:00 and missed the target frame. When pulling targets, someone said I should fire another shot for score as there were only four shots on paper. That is not what I thought was right, as I shot five shots and only four hit the paper. But I have been at informal shoots where misses were not scored. It depends on the match and the level of competition.
In other realms of shooting competition, I have seen small bore shooters fire from prone on to a sitting target, or from kneeling on to an offhand target. but they were never in contention to start. Poor sportsmanship.
I once shot a pistol match (law enforcement) when a couple of shooters added 6s to my target "just for fun".
ADK Bigfoot