So, the apartment is located in a very nice area that is close to the city center. The flexibility with check-in and check out times was extremely helpful - thank you very much. The guy and girl who live in the apartment were very nice and polite. We felt safe and had fun in DC.
The problem was that the host seemed to give her roommates short notice of our arrival, so when we arrived, we couldn't get in because nobody had left the keys in the place we had arranged to pick them up. We waited for about 50 minutes ringing the bell and calling the numbers they gave us, until someone who was home opened the door. Also, we were confused about who the host was, since it seemed that various people had messaged us prior to our arrival.
The house was less organized and clean than it seems in the picture. The kitchen was especially kinda messy and dirty. The worst part, I think, was that the bed linens smelled terribly when we got there, probably because someone left them wet in the washing machine for a long time before drying them. It made the entire room smell too. We tried opening the window to see if it got better, and ultimately sprayed perfume on them to be able to sleep more comfortably. I don't think they are bad people, or that other guests will always find the same kind of problems. I think they may have had an especially hard time preparing things for our arrival, and I hope the next guests have a better time.