I am going to try to give some information I would have liked to have before my trip. I will follow a temporary line since I arrived.
1. Arrival: it was arranged at 22.15. The person who had to give us the keys did not show up until 22.25-22.30. In normal conditions 10 minutes is nothing, but when it is nighttime and you are standing in the middle of the street and nobody replies to the WhatsApp messages or the phone calls and there is no message either on the Airbnb website warning about the delay, it is worrying. Even more, if there is an extra charge of 25€ due to the arrival time.
2. Accessibility: the flat is on the 5th floor, so you have two options: elevator or stairs. For a young person, it is not a problem, but it should be advised that the elevator is super small because it could be an issue for people with some disability.
3. Flat: there are many things to be mentioned here.
3.1 First of all, the floor. In the pictures, it seems to be new, all varnished and shiny. Very far from reality. The guy who gave us the keys told us it was better if we did not wear the shoes at the flat because of the noise. Only one hour after we arrived, the neighbour from downstairs came to complain about the noise, saying that every step on that floor makes a terrible noise at his place. He was very polite and seemed to be exhausted by people renting the flat on Airbnb. I don't blame him, but we were just walking and unpacking, so it was shocking to receive a complaint only after one hour. But then you realise that neighbour is completely right, every five steps you take, two creak a lot.
3.2 Bathroom: one of the doors in the shower is broken, nobody told us anything and it seemed to be like that for a long time. The pipe that collects the water from the shower was stuck. Only 1-2 minutes after you start having a shower, it overflows, and you have to be quick if you don't want to spill it all over the place.
3.3 Sofa bed: you don't expect to have the best dreams in a sofa bed, but something better than a 10cm thick and dirty mattress is way below the expectations.
3.4 Terrace: it is great, and the views are incredible, it feels like being on a movie set in Paris.
3.5 Flat in general: I have had the chance to travel many times to Paris and I have always found very tiny and dark apartments. This one surprised me in a good way, it is spacious and very illuminated.
4. Kitchen: we did not use it but it seemed to be very well equipped.
5. Cleaning: it was not too dirty but it was far from being gleaming. We found food in the fridge and some toothpaste from previous guests. It would not have been bad either to clean with bleach the WC.
6. Check-out: they were very kind and flexible. I requested to leave later and they did not put any problem, allowing me to stay three more hours which helped a lot.
7. Location: it is perfect. 2 minutes away from a metro station and 10 minutes walking from Notre Dame.
Overall, the flat is not bad. It has great potential but it seems to be neglected. They do not invest any single euro to repair basic stuff. When you travel to Paris you know it is a very expensive city, and we did not expect any luxury at all, but there are some basics which should be not negotiable.