Upon our arrival, it turned out that the air conditioning had stopped working, and there were some problems with the toilet. Christos reacted immediately and called his maintenance guy. Also he transferred us to his other apartment, which was located on the top floor and was completely identical to this one.
Both apartments are furnished beautifully, everything was new and squeaky clean! I especially loved the interior design combinations - there were original pop/modern art pieces on the walls, and the colors of the furtniture were matched to some details from these paintings.
The location is amazing: you are straight across from Saint Demetrius church - one of the Thessaloniki's hystorical symbols. Also, 5 mins walk to great shopping and dining areas; and 15 mins walk to the promenade, the White Tower, and the Aristotle Statue.
Christos was reachable at all times. We mostly communicated through the app, and he never took more than 15 mins to respond.
Something to note is that August is definitely not the best time to visit Thessaloniki. Even with great air conditioning, it's still very very hot. Also, even though the town was busy and full of tourists, some coffee shops and restaurants were closed (taking their summer break). So don't be surprised if Foursquare takes you to an empty and locked bar or coffee place. It happened to us three times. Of course, this doesn't have anything to do with my review, it's just a travel tip. If I could go back in time, I would have visited in April or May.