But what if you don’t know? Look at her finger and see if she wears a ring. And if you cannot see, well, then the following may help you:
If the woman is under, say 25, especially if she looks young, mademoiselle is fine. But if you are a man, and say "Bonjour Mademoiselle" to a 45 year-old, you could sound flirtatious.
So, over 30, it’s better to use madame. Some old "bigotte" (church mouse) might correct you bitterly, but it's pretty unlikely. On the contrary, if the said fourty-five-year-old woman answers with a smile “Mademoiselle”, she is flirting with you!
