Well, first of all they both speak fluent English, and they were very responsive to our phone calls and emails. Additionally they greeted us warmly and provided info on the local restaurants and the local train service. They set up our cab pick up for us when we were leaving which was very helpful.
The neighborhood was very quiet and there was a park right across the street. The U-Bahn station was very close which made traveling very convenient.
The apartment was very clean and spacious with high ceilings, a balcony, and very contemporary furnishings. The kitchen was stocked with gourmet coffee and tea, a nice coffee maker, and all types of dishware. There was also a nice refrigerator. We were very pleased with this place and we'd definitely go there again when visiting Berlin.