If you see someone running from zeds, and you're a reasonable distance away: Cap his knees, or head if you're merciful, and loot him after the zombies have had their fill. Why risk getting mauled by a zombie when you can just have them kill people for you? On a more serious note, always keep an eye on your surroundings, never approach flares without scouting around first and never let players see you before they've assured you to your satisfaction that they won't shoot you in the face. (Or don't approach players at all.)