Why must the degree vary?

When you’re in a new city, how do you decide who’s more of a stranger?
The one who randomly approached you somewhere or the one who initiated a conversation at work?
Come to think of it, are both not in the same category?
Why then do you believe and trust someone who meets you in familiar surroundings, say your workplace, or at a friend’s party but be suspicious and wary of the one who approaches you at a coffee shop or a bar?
How come the one who approaches you on the street or a Barista is more of a stranger than the one who showed interest in you at work?
Is it not a possibility that the stranger you trusted because the surroundings were familiar betrays you as opposed to the other one who may be totally harmless.
In a new city, how do you decide who is more of a stranger.
Is everyone not one?