I gave this place a 3 star rating for 3 specific reasons: the door, shower and wifi.
1. Door: to enter the apartment, you have to type an access code. It takes frustratingly multiple tries for the code to go through to unlock the door;
2. Shower: there's no curtain. With the detachable shower head, it was hard not to end up with a messy wet floor. We stayed at 4 different places in Nice, Cergy, Cergy-Pontoise and Paris, and noticed all of them shower with no curtains. Maybe, that's just how it is in Airbnbs in France.
3: Wifi: the wifi wouldn't connect on the first day; I called reception and they somewhat fixed it on the next day. The verdict is the wifi/internet connection sporadically functioned.
Despite the 3 minor inconveniences I above listed , we enjoyed our stay at Sebastien's apartment. The apartment's location is convenient and fantastic; it's within walking distance to Arc de Triomphe, Avenue des Champs Elysées, Eiffel Tower, shops, grocery stores, restaurants, etc.
The check in and check out process was smooth and easy; the host was available, responsive, courteous. But for the 3 first-world problems I above listed, I would have given this place a 5 star rating.