I will always call my own fouls, and if it is close I will ask for a ref to watch. Our hall owner is a certified BCA ref, and has done reffing in Vegas when he is there. He will come over and ref for anyone in the hall even on a just for fun set. mm self respect and integrity is worth more to me than a few bucks.
I typically only play with folks i know and like. I will often let my opponent know their potential error ahead of time. I suppose it is more habit than anything, since i use to play with someone who always drank too much, and would always make mistakes. it was easier to correct them than win every game by default. Now I do it on instinct.
what it boils down to for me is :
if you know you fouled, i think you should call yourself. if you deliberately cheat and are known for not calling your own fouls i probably would avoid playing a rack.
if you see your opponent is about to foul, well, that is all situational. you are not responsible for them, but perhaps you know they are a new player, or you like them as a person so you decide to help them out.