I always use ma'am or sir. It's just the simplest way to show respect. If someone thinks I am making them feel old, I reply with "oh no, ma'am has nothing to do with age, it's a respect thing." That is usually well accepted. Just happened on the phone with a woman that works at our corporate office a few weeks ago. I always use ma'am and one day she laughed and said she felt old becuase of all the ma'ams. I told her it had nothing to do with age, and I wish she were used to being talked to with more respect. She appreciated what I had to say. In business, I say ma'am and sir to everyone I deal with. I don't think ANY of my clients or vendors have any problem with it. To argue that sir or ma'am is offensive just doesn't make sense to me. Some people might not be used to it, but to claim that it's offensive... I just don't buy it.