It pains me to say this, but Customer Service is not a strong suit in Paris. French companies want you to believe that customer service is important to them, but the fact is, it is not part of their DNA. I recently tried to reach my cell phone provider (a company which vaunts itself as being n°l in Customer Service). After all options were exhausted and the system promised to put me in contact with a human being, a recording announced that this is not possible right now, and – I’m not kidding -do not call back any time soon. But I digress.
You may well have a pleasant experience, perhaps because you have followed my advice (see Manners n°24 and Smiling n°42) but here is my point: if a waiter is at best indifferent, if a salesperson would rather continue talking with their colleague than acknowledge your presence, or worse, if they act as if they are Doing You a Favor to sell you their wares, do not take this personally. These people are not being rude because it is you, they are rude to everyone! This simple insight should allow you to rise above or look through unpleasant behavior.
Now, about Tips. In France, a 15% tip is included in the price of anything that you consume. You will sometimes see a mention service compris. This means that you do not have to leave a tip in a cafe or restaurant. Here is my rule: if the service was not great, I do not leave anything extra on the table. On the other hand, if the waiter or waitress was pleasant, nice, helpful, whatever, then I leave a bit of change, for example, the small gold coins plus one euro per person for an inexpensive meal.
When I take a taxi, I give the driver about 10% if the ride has been pleasant.