My girlfriend and I stayed in Claire's apartment for two months. The flat is located in the 18th arrondissement, very close to Metro Marcadet Poissonnier. It is situated at the 5th floor with no elevator (quite common for old Parisian buildings). At the check-in Claire was not there, we took the key from a supermarket locker.
The apartment is well decorated, there is also some quality furniture, we appreciated especially the sofa in the living room.
When we arrived everything was clean except the fridge and the oven (we cleaned the fridge, but the oven was more difficult to clean and we preferred not to use it).
Internet often didn't work, according to Claire there was nothing that could be done. She said that she's was going to change Internet provider after our stay.
All rooms give to a quite busy intersection of many streets, which are inevitably noisy (especially due to ambulances and police), but the double glass windows help a lot in reducing the noise. On the other hand, there is no indoor acoustic isolation, we had in a few occasions minor issues with music and similar, but nothing serious.
Regarding the check-out, we did it with the boyfriend of Claire's sister and everything went smoothly.
Overall, the value for money of our stay was quite good, especially considering the relatively low price for Paris (around 1000 euros per month, AirBnB fee excluded).