The idea that “the customer is always right” was invented in the US. Although, this notion of customer service is becoming more common in Paris, it is still a “foreign” concept. That’s not to say that there aren’t countless proud shopkeepers that value their customers and show them plenty of kindness. But their treatment of you is more driven by personality than by societal expectations.
In France, the ideals of the French Revolution are alive and well: liberty, equality, and fraternity. It is not seen as necessary or dignified to act subservient to a customer. The customer is seen as an equal, no more important than the shopkeeper. If the customer wants to be treated with respect, then they must in turn treat the shopkeeper with respect.
If a tourist enters a shop expecting to be catered to and without observing the proper etiquette, then they may be in for a frustrating experience. However, if you say “Bonjour” upon entering, don’t fondle the merchandise, and politely say “Excusez-moi, Mademoiselle” when you want to get the shopkeeper’s attention, then you will likely fair better. But, remember, they aren’t “serving” you. They are allowing you to purchase their merchandise.
One more thing, don’t expect a receipt. You may get one, you may not. People simply don’t return things in France. We bought a piece of luggage at a department store in Paris and never got a receipt. It’s just a different way of doing things. C’est normal!