Communication with Carlos from the beginning was easy and he answered all of the questions I had before arriving in Madrid.
In his apartment, I was welcomed by his brother who showed me the place and gave me all the information I might need during my stay. I didn't get to meet Carlos, but his brother was really nice and always ready to help with anything I needed.
The room is exactly as it is shown in the pictures, and when it comes to the apartment, it was kept clean during the two weeks of my stay. Also, it is nice and quiet, and the location is great. I was looking for a place close to Atocha (approximately 20 minutes away on foot), but it is also connected with buses and metro lines with the center and other areas of Madrid.
I would recommend staying at Carlos's place. :)