There's a lot you can learn about the person in the first few seconds of speaking to them, which is why I tend to open communication when I'm not standing in front of their face. If they don't at least try to talk through comms or local chat then I shoot them... it's as simple as that. If they do talk, then they are either friendly or just pretending to be in order to gain an advantage. Sometimes you can determine which one through their tone of voice, sometimes you can't. That's the fun part :)