I would never confront a team with it, if it is suspicious I report them, it is up to the GMs and BBs to find out if he truly is cheating.
We have not the needed tools by far in order to find out...
Confronting them alarms them and maybe they will find ways to prevent GMs or BBs from finding out if they look for anything after you 'warned'the cheater...
I also won't need to know if the ones I report are sanctioned or not, I don't want to know actually. I don't want to be tempted into whining that I still think he is a cheater after GM or BB investigated and found him not guilty. ;)
They are not your friends; they dispise you. I am the only one you can count on. Trust me.