The fox seems to have the uncanny ability to tell the difference.
Though they are an extremely shy and cautious animal, foxes will often approach a person if the person is well-meaning and remains still. However, there has not been one instance of someone who was hunting ever having been approached by a fox.
A story told by Stephen J. Krasemann shows how friendly foxes can be. He was photographing a family of foxes on an Alaskan peninsula.
After only a few days, the foxes came quite near to him and seemed to adopt him. On the day he was to leave the area, the dominant male fox came over and put a dead rodent at his feet. When Krasemann didn’t pick it up immediately, the fox pushed it closer with its nose and finally dropped it on top of his feet.
Some farmers think foxes kill chickens, but studies have shown this to be a rare occurrence. The main food of the fox is rodents.