For example if Player1 tells you that Player2 was mean, just tell Player1 she/he can mute Player2 and file an abuse report. If you did not see it in Global, isle, here, or near, or buddy, then it did not happen as far as you are concerned.
Many times it did not happen. Player1 was just trying to get Player2 into trouble. Or Player1 misunderstood Player2.
So when you PM Player2 and say "Please do not be mean to others, what you said to Player1 was not nice." That doesn't work. Player2 may not have even spoken to Player1. So, you end up harassing players.
Just be careful. Hearsay is usually incorrect.