It was all fine. The apartment is nice and clean and is located in the very center. Also the directions to the airport as well as some basic but very useful informations were provided before our arrival.
The wifi was not working. However this seemed to be a general problem in Istanbul.
If you are 5 persons who want to take a shower one after the other, for the last two there might not be any hot water left.
Overall we were very happy with our accommodation.