From what I've seen, most people with a decked out M4 and Ballistics Helmet hanging around area's where they really have no reason to be is a clear sign that he's probably not looking for a friend. I tend to trust those in helmets less than say a nice beret, but that's just me. And I can't remember what the mod was for DayZ Mod, but there was one where if you put your cross-hairs over a player you would hear a heart-beat. The faster it was, the more people they killed. The system didn't judge whether it was a bandit, hero or new spawn, the more you killed, the faster your heart-beat. I think something as vague as that is perfect for the standalone, because you don't base your entire decision on the heart rate when you look at them, its also what they may wear or how they might act that determines your final decision on whether to take a shot or not. All the heart rate is is just one more small piece of information to help your final decision.