The appartement is nicely furnished and has a nice outside area where you can relax / drink and smoke. The room itself has a big comfortable bed, with the speciality that it's very silent during the night because the window is heading towards the backyard - definitely a rare thing in Istanbul.
The location is also very good, in about 5 min of walking you can reach the centre of Besiktas where it's always busy and many restaurants / bars can be found. A Supermarket is directly besides the house, and bus stops are very close nearby.
Defne is a very friendly and helpful person, I had no problems with her at all. Hope she had none with me either :)