That's SUCH a dangerous line

Some women will get offended if you call them Ma'am... because it makes them feel old. Some women will feel you're being disrespectful if you call them Miss... that you don't think enough of them to call them Ma'am.
My general rule (and I don't know how this applies in other parts of the country... this is the North, this could get me blacklisted in the South I suppose) is that if the woman is older than me, or married, she is Ma'am. If she's younger than me, she's Miss.
Use at your own risk