I think this a question that is very central to writing, and I guess every writer has a very personal approach of how to come up with characters.
First of all: If writing was always autobiographical, then I can only hope I'll never meet the writer of American Psycho.
Having said that, I'll say that I piece together characters using my imagination and my memory - and that can
mean that I refer to situations or conversations that I have witnessed or experienced myself, or to views that are my own.
But I'm more proud of characters that I personally disagree
with, because writing against your own beliefs and still make it consistent and believable is more difficult and therefore more challenging.
The antique shop owner makes a lot of good points in his dialogue, I agree with much of it, but not with all of it. He's very much stuck in the past, and very bitter.