Karsten was a great host, very friendly and welcoming. We had a couple of minor issues and he was very quick to help. We had a little change in plans and had to travel with our baby last minute and Karsten was very nice about it, arranging a baby bed and a chair and everything we needed.
The apartment was also great. Very clean and neat, nicely decorated, very comfortably located just down the street from the subway station.
Had everything we needed for a great stay in Berlin!