Marta's place is beautiful - very well decorated, the location is OK (20 minutes walk from Plaza de España, close to the subway and buses) and great for a weekend with friends. Marta was also really great when communicating initially, accommodating my requests and a change in the booking.
However, when you get there you will be met by Olga: she was late and didn't reply to our texts and then claimed we were late and we had to pay the 30 euros extra for checking in after 8pm. We tried to call her multiple times before 8pm and she only picked up after 8pm. She was also not responsive at all - we had a problem with a key that she really didn't care about and never reply to my texts to confirm what the checkout procedure was. She was also rude towards me and my friends and made us feel uncomfortable by asking way too many challenging questions on politics and the history of the city. Overall a very good experience with the apartment, but not good with the host in charge, at all.