Just to further the subject of street photography....thanks to the folks at duckrabbit for posting this video link with street photographer Matt Stuart.
His quote, "Invisibility would be my superpower," is excellent, but I think the key thing to learn here is the way he carries himself while photographing. His demeanour is unthreatening because he is confident that he is doing nothing wrong, and certainly no harm to anyone. I agree completely that people sense whether you can be trusted or not, and you have to project that they have nothing to fear from you.
I see so many young photographers trying to work, while being almost frozen with fear that someone might ask them what they are doing? Why are they photographing them? If you know in your heart that individuals have nothing to fear from what you are doing, it really isn't too difficult to explain yourself in a unthreatening manner.
I also can relate completely to his words about being among people on the street and sharing a moment with them, without them ever realizing it. We are very privileged in what we do because of all of the moments we get to experience - all of the emotions, both good and bad.