The location! it is very central, yet quit! No noise at all, 1 mins walk to Metro and bus stations. The apartment is very clean with everything you would ever want. I stayed for 2 nights, but I wouldn't mind staying there for months!
On the other hand Berk is a very decent person. I did the booking only 12 hours before arriving, yet Berk was very responsive when I messaged him. Bottom line, Berks place is highly recommended..