That's why I'm somewhat selective about who I play with. We'll concede putts that are meaningless in a team event (like if his teammate is already in with par and he has a 2-footer for par) or if it's within a foot. Which is generally expected in matchplay format.
We learned a long time ago that (in our group) we either play by the rules or we don't play. It prevents petty arguments and saves a lot of grief and frustration. How others play their matches really doesn't concern me. To each their own.
I just know that when tournaments come around - I've got a legit handicap and a pretty good handle on the most routine rules that come into play. There are some that can be a bit more complicated, but for the most part we really don't run into too many problems with guys cheating. They know it's not tolerated, and it's a reputation no one wants.