I stayed at Sersah's place for slightly less than a month. It was my home base for the month of August while I visited Istanbul, and a couple of other places in Europe. Firstly, Sersah was very communicative from the time of booking through arrival. My flight landed at 4 am (-_-), so I stayed at the airport for a couple of hours as check-in was not until closer to 11. Around 9, he checked in and upon learning I was sitting at the airport he told me to come on through -- which was nice because I really wanted to nap in a bed. Sersah met me at the door and helped take my luggage upstairs. FAIR WARNING -- there is currently no elevator in the building so, keep that in mind. You will certainly get a workout for your legs on the daily :-).
In any case, the apartment itself was gorgeous, and of course i loved the swing in the middle of the living room. It's very nicely decorated -- large windows, lots of natural light. It was exceptionally hot (for me) during August -- another thing to keep in mind. The apartment is on a ..what i would consider a busy (and fun street). If you have trouble sleeping with noise, this is not the place for you. It took me a couple of days to get used to it, but after a couple of days -- I can get used to anything. The location, absent the noise, is very ideal. I enjoyed watching the night life from upstairs. You can get to any number of cafes/restaurants in Kadikoy with ease. It's about a 10-12 minute walk to the ferry -- it really is a convenient location. I highly recommend staying in a less touristy area if visiting Istanbul -- and Kadikoy did not disappoint. The apartment is so spacious -- i mean 4-5 people easy, if allowed. Both bedrooms are quite sizeable, wood floors -- again lots of light!
Sersah and communication -- no complaints. He responded to any questions I had within a reasonable time frame...a few minutes to half hour. Nothing was really urgent. He explained everything before he left that morning when i arrived.
I would stay again if i had the option to. 5 stars.