If you find Demetris' place available on your required dates, just book already.
I bet you won't find any place that is better than his at the same amount you pay.
So to start with, the studio is located in the Kerameikos area, around 5min walk from the subway that will take only one station ride to where all the famous artifacts await. Also, the area itself is pretty cool with all the fancy eating and drinking places around. The studio is very clean, larger than I initially expected from the pics. The air conditioning works well, which really matters when staying in Athens in the summertime, the kitchen has everything you might need if you are going to cook. Also for some unexpected surprises, Demetris will prepare the place with all the amenities including the capsule coffee, shampoo etc and even bottles of water in the fridge. I honestly never met any host who prepared to receive a guest in this dedicated manner. He will be super fast in replying to your inquiries, it usually won't take more than ten minutes. Although I didn't get to meet him in person, I could see from his messages that he was very warm-hearted. The only glitch would be the no elevator everyone is mentioning and apart from that, a window inside the bathroom wouldn't lock but I had no problem with it and II am pretty sure he will take care of it soon as possible. I would definitely go back to his place if I am to revisit Athens.