I've never had a bad experience with AirBnB until this time. I am still on vacation as I write this but wanted to note this before I forget.
It is also worth saying my experience may be a one off because this host and place generally gets high marks.
The Good:
I loved the location. Very walkable to all major sites. Also in a diverse area, LGBT, lots of different kinds of ethnic foods, etc. Area felt safe to me.
The flat itself was on small side but fine for a single or maybe a couple.
It was warm at times and there a fan and a quasi-AC machine but a tube or duct ran from the outside and it blew dust and smells from the construction outside into the apartment. Not cool. I can imagine summers being terrible in this flat.
The Bad:
Two major things. First, the host was not available so they had someone else. Not an issue. I've done AirBnB plenty of times and never met the "true" host. They had someone else meet me. Scheduled to meet around 3. We met at 330. After the longest flight from Los Angeles I was ready to shower and unpack. The apartment was not yet available; had to be cleaned. They said maybe 1-2 hours. I had to leave luggage and walk around for a while. At 430 no message (thank goodness I had intl data plan to receive messages). At 530pm no messages. I finally message the host at 600pm asking what is happening and she apologizes saying the flat/apartment is ready, more than 2.5 hours after it should have been ready hours earlier. She said sorry I didn't mention it earlier... I shouldn't have to follow up...
Second, there was construction next door, which I was not made aware of. Every morning there was loud noises. And dust and smoke. And the smell of wood being cut and sawed. There are windows to the apartment. Because the apartment is so small, leaving windows open is ideal. There's two fans, one with an AC option. The quasi- AC fan was connected to a tube or duct, to the outside through a window. That prevented me from closing the window no matter what. If turned on the AC machine it blew dust and smells more directly into the apartment. If I didn't, I still had the air fan. But I didn't have the option of closing the windows to block out the dust/smells/noise. It was very frustrating!
Overall: I would NOT stay here again. And I really love AirBnB and enjoyed my time in Madrid despite my bad lodging experience. :(