It depends, you have to read the situation. When I was new, I murdered another fresh spawn, I felt sooo bad! If I'm alone and dont have a lot to lose I try to be friendly. I will counter fire for sure. Last night I was with a friend, he had a broken leg, so we were looking for Morphine. We get to the top of Green mnt. He asks if some one is around and can help, no response. We know some one is near by, we heard gun shots. My broken legged friend is near the front front gate asking for help. I looped around the fence and go to the backend of the camp and crawl through a small hole. I see a guy aiming at my friend, so I go full auto on him. He goes down. I didnt feel bad about this, I feel since he didnt communicate with us and was aiming at a friend, I was justified in killing him. Most of the time, I try not to shoot other players, I will lay and watch what the other player does and my actions result on what they do.