It's just a matter of who you are and how you talk to people. Your subjects will trust you only if you're confident about what you're doing. It really bothers me when photographers first approach a subject without a camera, try to establish a personal relationship, and only then get out their cameras. It's deceptive. I think you should just show up with a camera, to make your intentions clear. People will either accept you or they won't.
Mary Ellen Mark