From a Paris guru:
Perhaps the most important thing in Paris is to observe 'la politesse'.
.
ALWAYS start with 'Bonjour Madame/ Mademoiselle/ Monsieur.' And say 'Au revoir' Madame/ Mademoiselle/ Monsieur' as you leave the store. I have learned through many visits that the French formality is cultural, rather than a coolness towards outsiders.
