I'm American, so for me, tipping feels polite and appreciative. However, as a good traveler, I also know that the customs in my home are not necessarily the same in the places I travel. I dont want to totally disrespect local customs.
I'm arriving in Paris with my family on Christmas morning (December 25), and we're renting an apartment through one of the popular (and legal) agencies, at the outskirts of the Marais, across the boulevard from the 11th. The agency offers to have groceries waiting for you, but this service is unavailable on Christmas Day. The "greeter" of the apartment recently emailed me to ask if we have any questions prior to our arrival. I asked about groceries, not knowing the agency doesn't offer that service on Christmas Day. She replied that she will be happy to buy groceries for us and have them in the apartment when we arrive.
That's very nice of her to offer to do that. In addition to reimbursing her for the groceries, my impulse is to thank her with a cash tip on top of the cost of the groceries. If your response is something like "that's not necessary" then I will do it anyway, because it will make me feel good to tangibly thank her beyond a heartfelt "merci beaucoup." HOWEVER, if your response is that my offering a cash tip would be rude or would cause her discomfort or would be negative in any way, then of course I want to respect the local custom.
I just want to do the right thing, and I don't want to offend her. What wisdom can you share with me? THANK YOU!