My girlfriend and I stayed at Claire & Xavier's place for 3 nights recently.
In general, it was a pretty nice stay. The apartment is really well located, few steps walking from the subway station, also close to the Bastille and to some good restaurants, supermarket, pharmacies and also not much far from the louvre - you can go walking. Le Marais and Paris are amazing!
I sent some e-mails to Xavier before we arrived, and he always replied promptly our e-mails, so the communication, at first, wasn't a problem. Actually, it was really good.
The only thing that made us call him to ask for, was a problem during the shower. The winter in Paris is really cold, and a hot shower is - at least for us - really important to start the day. But we didn't know that there was a limited amount of hot water in the apartment (my girlfriend took a 15min shower, and when i started my bath (about 5-7 mins) the water became freaking cold - and stayed cold). I had to call Xavier, and he was very attentive, and in a few minutes he arrived in the apartment trying to solve our problem. It wasn't possible to solve because there wasn't hot water in the tank anymore - we had to wait untill the night to have hot water again, and i had to finish my freezing shower). He said that this had never happened before, and i understand that, i felt ok because he really wanted to help us. I just want to suggest that, now that it happened and we know that, this information could be written in the general information about the apartment, to avoid other people to be in this same situation.
We just had a problem in the last day, for a misunderstood - i haven't paid attention to the check-out time and, because of that, we got almost 3 hours late. I've assumed my fault and paid extra for it, so, i hope we're ok now.