In order for a game to truly exploit trust, there has to be an option to not trust a character in your party and potentially get rid of them early on based on your personal distrust. Even in games where it is blatantly obvious that the Snidley Whiplash-looking character you're traveling with is going to try and kill you, you're forced to work with them because the storyline demands it. More games need to give you the option to say, "Screw this guy, he's obviously going to stab me in the back." Then to go along with it, they'll have to give you plausible reasons to keep the person in the party despite your audience knowledge. Or, OR... Do a better job of hiding Snidley's treachery. Maybe shave off his moustache and get him some posture-correcting back brace.
That's all as far as I'm concerned. Either make it a lot less obvious that someone's going to betray you, or give me the option to kick them out of the party early on.