I always address my clients the first time as Mr and Mrs. unless I have been informed one is a Dr. then Dr. so and so. Unfortunately, you can still get in trouble with even that. They want to be called by their first name and are offended that you are being so formal with them. Gah! I live in Colorado and I swear no matter their age, they all go by their first name. The few who don't, well they are cranky about lots of things, not just their name, lol.