So far our experience with cheaters has been pretty minimal but it has existed in every single tournament we've played in to one degree or another. For the most part it's been with other groups so we haven't had to call it out. But a couple of buddies who are also golf dads have gotten into it with other dads/caddies over blatant rule violations (ex: foot wedge, illegal drops, grounding in bunkers, etc).
In a recent tournament I had another dad come up to me and warn me to count every shot for a girl playing in my daughter's group. I do this anyway - just a habit from playing in amateur tournaments myself - and have taught both of my kids to build this habit when they play in tournaments. Well sure enough that other girl tried multiple times to write down an incorrect score. On the 4th or 5th time I finally approached her dad/caddy and said "look I don't want to make this a big deal but if she's not going to write down the appropriate scores then she's going to end up getting herself DQ'd in bigger tournaments". He was visibly frustrated because he knew damn well what she was doing and was playing dumb but that was the last time she tried it in that tournament. Couple of weeks later I see that she finished in 2nd place in a bigger 2-day tournament. As I'm talking to the dad who's daughter eneded up winning he said "we didn't play with her on the first day but we did in the final round and she tried 5 or 6 times to shave strokes and we called her on it". Somehow on the same course in the same conditions she ends up shooting WAY worse on day two than she did on the first day. Weird how that works out.
My daugther also played a PGA sectional 9-hole event recently. These are fun events my kids use for practice so we never really take them super serious. My daughter gets paired up with a nice girl who she has played with lots of times. I only got to follow them for 3 holes but my wife tells me after the round that it was rake-and-place in all the bunkers because of some renovation work at the course and this girl kept building a little mound to place the ball on when in the bunkers. Basically teeing it up. End of the day it actually didn't favor her one bit during the round but I told my daughter that she's going to have to be vigilant in tournaments as she gets older and call kids on stuff like that, even if they are "friends".