So, some general advice.
Never trust somebody who doesn't put himself on a mission. If he's good, he is bettering the odds that the mission will succeed if he's on the team. If he's bad, he may be trying to avoid guilt for a mission failure by putting a cohort on the team with a bunch of good people, while remaining seemingly innocent himself.
If at any time you think to yourself "that last mission proved he's a good guy!" you have already lost the game. There is no proof of innocence, ever, there is only proof of guilt, and it's circumstantial and only probable.
At all times, you should be think to yourself "how am I being manipulated right now?" and then try to figure out who it is that's manipulating you, and why.
Remember that at least a third of the players making mission group proposals are doing so in bad faith, to better the cause of the bad guys. Vote accordingly. Make it difficult to pass proposals, so that bad guys cannot hide amongst those voting no.
The more votes there are, the more data there is. Data can be deceptive, but patterns can emerge at critical junctures. If two missions have been successful, the bad guys must vote in their own interest to prevent a loss.