Our experience in this apartment was largely positive. It's in an absolutely spectacular location in Madrid, in an old building with a lot of character, and is a good value. The host gave us exceptionally clear directions on how to get there and was very communicative throughout. And overall we quite enjoyed our stay. But there were a few negatives you should be aware of.
First, the apartment gets very little natural light. In the interior bedroom it's impossible to tell whether it's night or day; the glass brick window looks into the adjoining room, not outside.
Second, the large majority of light bulbs in the track lighting were broken (often with wires sticking out), making the whole place quite dark. The wooden bench had also been broken then repaired shabbily enough so that you wouldn't want to sit on parts of it.
Third, the small street that the apartment looks over can be extremely noisy at night. We live in New York City on quite busy streets, but this level of noise was on a different level. It only occurred on only a few nights, though.
Finally, the person who checked did not give clear instructions. He was also oddly reluctant to giving us more than the bare minimum of towels and toilet paper. And strangely, the people who came to clean the apartment after we left accused us of leaving the door open on our way out (we absolutely closed the door). They didn't claim anything was missing, though, and nothing came of this.