We didn't meet Marleen in person, but the instructions she left us were very detailed and easy to follow.
The flat is beautiful! It is very spacious and obviously recently remodeled. It was very clean and modern and the furnishings are very stylish. There's a chance we were the first guests, that's how new and clean it seemed. The WLAN worked very well.
The building itself is nice and has street art murals in the hallways. The location is fantastic - There is a U Bahn station right in front of the building and you can get anywhere in Berlin from there. Within walking distance you have many shops and restaurants, a large grocery store that is open late, massage parlours, and a clothes washing salon. That last one is important as there is no machine in the flat. However, the salon is nearby, clean, has WLAN, offers food and drinks, and has a friendly owner.
Overall this flat is great; it has the feel of a luxury hotel but with more privacy and a lower price.