Mert's place was an amazing stay and a great way to end my time in Turkey. It was extremely spacious and located nicely in Istanbul's Sisli area, which is close to the more modern/shopping parts of the city.
While I didn't meet Mert himself, check-in was very convenient and he handled it very well. He was great at communication, which was essential as a late flight meant me and my friend only made it to his place at midnight on the day we checked it. He was quick to respond to messages, which was very appreciated.
The place itself had tons of space, a nice comfortable couch, and additional bedding which was very convenient on the night we checked in. The bathroom had tons of space, and while the washing machine was a bit of a challenge to figure out (all labels in Turkish) it did it's job well.
Only note I'd add is the location - it's extremely challenging to find a cab from here on the weekend because of Istanbul's traffic, and this was an issue w/ both cabs and Ubers. While this is obviously a feature of the area and not the property, it's something you should keep in mind if you have time sensitive plans when staying here. However, barring this slight challenge, I'd go so far as to say it was an almost perfect stay in every other way - one of the best AirBnB's I've stayed in so far.