That's why I go with my gut most of the time.
-You follow me to a room where there is absolutely nothing, and turn around "just cause", I'm killing you without question.
-I hear a kos on you and find the dude dead seconds later, I'm killing you without hesitation.
-You're constantly pointing a gun at my face, I'm gonna shoot you.
Really, I don't care about karma. All it does is prevent me from killing the people who I know is Traitor.
I guess the best thing to do is not listen to anyone else (unless of course they're playing the game for real) and only do what your instincts tell you.