Overwhelmed by amount of rules, especially when other players don't know their own; unintentionally cheating. What to do?

Played an iron storm spearhead list and got destroyed, found out after the game he was playing his rules wrong and using the mercy is weakness strat.(W/target augury) on full strength units and during overwatch. Contemplated quitting the game after this; how often does this happen when rules are missed? There are so many different rules how do people keep track of them all and or avoid the players who don't know their own rules. It seems difficult to be reliable for your own rules and everyone else's too.