I stayed in Fabian's apartment for about 20 days during June, and my stay was excellent in all relevant aspects:
Communication: From the moment I first reached out to Fabian, our communication was cordial, fast, and precise (he speaks perfect English, which was great given that my German is quite limited). Fabian did not only answer most of my questions within 24-36 hours, but he also went above and beyond to accommodate some of my needs (i.e. early check-in, and stuff like that). Once at the apartment, he also made himself available to answer any question I had. He was, at all times, friendly and cordial.
Accuracy: The actual apartment is exactly as shown in the photos; and if anything, I would say the guest room is a bit bigger than it looks on the picture (perfect for 1, maybe a bit tight for 2). The apartment is clean, very nicely decorated, has a great bathroom exclusive for airbnb guest, and has a very functional kitchen with everything you might need. In addition, the balcony serves as a perfect spot to spend time in the afternoon, specially during summer.
Location: The neighborhood is up and coming -it might not be at the very center of Berlin, but it has all the necessary services (a great supermarket, a Cafe, etc.) within 3 minutes walking distance. Additionally, the apartment is about 10ish minutes walking from the Hauptbahnhof, Berlin's main station from which you can get to anywhere in the city, as well as to anywhere in Germany. That said, I also enjoyed the neighborhood itself, specially the riverside for running; and if you take that route and cross to the other side to the Invalidenfriedhof, you might get to see one of the largest -and mostly unaltered- remnants of the Berlin Wall.
Overall, I had a great stay at Fabian's apartment, and I would definitely recommend it.