Judgement. Some dogs can also sense when their owners are coming home or if there’s any danger. So it makes sense that we trust their judgement when they begin to act strange around new people.
Distrust. If our regularly polite dogs suddenly can’t stop growling at a new person, we can’t help but immediately distrust them. And that makes complete sense because according to science dogs can tell when people are bad or not.
Studies. Multiple studies have found that dogs can tell if a person is untrustworthy or not. In a more recent study, researchers asked dog owners to try and open a container, and then ask for help from two other researchers.