You can, at the first point of contact, assume that everyone you meet is an enemy. Ala; Deathmatch. Unlike Deathmatch games, most people in DayZ wont open up on the person as soon as they see them. They lock eyes, have a thousand situations run through their mind then back away as quickly as possible. All the while reluctant to open up on the other guy who might just want to crack your skull open and steal your beans (In your backpack, not your skull. If it's the former then he's a Zed). I love DayZ for that reason. Such a strong reluctance to shoot another play, who at the end of the day if we're honest, will have no impact on my personal life once I walk away from the PC. It's crazy.