When traveling, it’s always a good idea to be polite. It doesn’t matter if you’re going wine tasting, visiting a museum in San Francisco, or shopping in Paris. After all, you’re in their territory.
Typically in Europe, and especially in Paris it’s a good idea to greet the shopkeepers when entering a shop and to thank them when you leave. Why? It’s just the polite thing to do. You also get to practice your French or Italian or wherever you are.
In fact, practicing some simple phrases in the language of the country where you will be visiting is also a good idea. Start now by learning ‘hello’, ‘goodbye’, ‘please’, and ‘thank you’. You’ll be glad you did.