The French can be quite sticky when it comes to manners and etiquette. The rules and protocol are a challenge for most visitors and we were no exception.
On entering a small shop it is considered polite to greet the shop assistant and in some cases even other customers. Otherwise you always exchange greetings when you get to "the till".
It is considered impolite to say "bonjour" without following it with "monsieur" or "madame". The french equivalent of "Have a Nice Day" is another interesting little etiquette minefield.