Can dogs sense when a person is a bad person?

[kurtcagle]

14. Smell and body language

Dogs can smell pheromones, including those produced by fear (either in their owners or in strangers interacting with their owners), but they also react to the body language of the "alpha" of their pack, which is usually the owner. They are usually also sensitive to people who are sick (such as with cancer), as this changes the body chemistry in enough ways to change how people smell. They're also usually more predisposed to be protective of their owner's "pack", again, determined by the scents that related people have.

I've often found that, when confronted by a dog, the best thing you can do is to put your hand out, palm down, and let them sniff you while acting in a non-threatening manner. If they still act aggressive, then moving into a non-threatening stance is best, while not running away.