We absolutely enjoyed our stay at Sedat's apartment and highly recommend his place.
Location. The apartment is a short walk from the Grand Bazaar and nearest tram station, and is about a 15 min walk to the nearest metro. There is a small phone shop next to the Western Union right across from the apartment, where you can get a great deal for a sim card. There are also many supermarkets and restaurants in the neighborhood.
Apartment. Sedat's apartment description and pictures are accurate. Located in a historic neighborhood, the apartment itself has been renovated and is very comfortable. The room is on the top floor of the apartment complex and is bright with panoramic view. The bed is amazing, shower hot, and there are kitchen equipment for cooking; wifi is good. Cleaning is done regularly during your stay, and laundry service is offered as well. Keep in mind that the apartment does not have an elevator so you will be taking the stairs.
Host. Sedat is an incredible host -- very communicative, responsive, helpful, and is always there for you for any questions, recommendations, or any other help/ assistance you may need. We especially loved that he kindly let us store our extra luggage for a few days while we visited Cappadocia.
Overall a great place to stay for you visit to Istanbul!