I travelled to Deniz's apartment with 6 friends and we had a wonderful stay. The apartment was very clean and well stocked and had lots of space for all of us. The bedrooms in particular are very spacious.
Deniz was very easy to contact and although she could not meet us on the day, the friend we met was very prompt and had lots of info about the city.
All in all it was a easy process and a solid recommendation if you happening to be visiting Instanbul!