DayZ is pretty wild. I watched a guy get jacked by bandits, another guy run up to help and only get shot at and bait the zombies. After he ran away along with bandits I hid in a nearby house by the first guy's body. When the bandits returned I opened up on them from a window. They never saw it coming.
Unless I play with RL friends, I'm not teaming up with anyone in DayZ. I won't be a bandit but I will kill them on sight given a good opportunity. Otherwise I'll be in ninja mode.