While it used to be customary to formally greet shopkeepers in France with, "Bonjour, Madame," or "Bonjour, Mademoiselle," nowadays, to simply say "Bonjour" is fine. Of course, a little formality never hurt! Feel free to say "Bonjour, Madame" to a woman, or "Bonjour, Mademoiselle" to a teenage girl.
Thinking of a trip to France? For up-to-the-minute hotel and restaurant recommendations, plus the best planning advice, check out our online France Travel Guide.