I don't know of a way to measure being an effective Mentor. Its like Commendations, can be skewed if people take the time to manip the system, or like Gold Saucer card and Minion tournaments, where people use alts or friends to get "cheap" victories to guarantee themselves Wins.

Honestly i think for GS Content, you should have the option up front to Choose whether you will be be battling PCs or NPCs, and you are restricted by that for that given tournament, so that people who abuse "cheap" methods aren't grouped with people who just do NPC battles.

Anything is able to be manipulated. A person could write a macro to "explain" a dungeon mechanics if they instituted something where if "key words" were said in the run, it would count as 1 point towards being a mentor. Or if fast response/lack of AFK/Kill credit was all part of it, it would be a bit more challenging for an idle person to get credit.

I think the commendation systems needs to have a bit more reward also. I am sure i am not alone in this either. But the first 5 instances i do a week, i am about 10 times more likely to give a commendation than i am the rest of the week due to the challenge log. But i also know its a rough balance. Give something too good, and people will just spam easy stuff to build up their commendations.

All in all, it boils down to an Honor system, and Luck. Sometimes you get the players who want to actually help, Other times, and sadly more often, you get the players who just shout "Mush" and want to speed through stuff without regards for others.
I am not saying either is wrong. Its just perspective. Everyone pays the same amount, so there is no "wrong" thing here. Just perceptions of morally right and wrong.