I stayed at Marc's place with my partner and our two small children for six days this summer. We wanted to stay in Prenzlauerberg, because we had heard it was a great location to stay in Berlin with family. Marc's flat was in a perfect location - close to public transportation, shops, restaurants, grocery stores, and parks. Although it was lively, it was quiet up in our apartment. And it was wonderful to have so much space with so many of us.
We never actually communicated with Marc, but with Jorg, the property manager. The company manages 35 or so properties around Berlin. Check in was great, and we met with a lovely lady who was on time, friendly, provided us with lots of information, and even helped us with our bags.
I would describe the flat as "fairly clean" - the dishes in the cupboard were dirty, as was a towel in the bathroom, but other than that, it was good.
Upon choosing a place to stay, I wanted to make sure we had a washing machine, as we didn't want to bring too many things along. We quickly found out that the washer was broken (the "service" light was on when we arrived), which was a huge disappointment. I contacted Jorg by email, and when I didn't hear back, by phone and he answered right away. He got back to me later, telling me that he couldn't get someone to come and look at the washer until the day before we left - very inconvenient for us. On top of that, our clothes were trapped in the washer (which we finally managed to get out on our own).
There were a couple other things that could have made our stay better: we were responsible for purchasing everything for the apartment ourselves (e.g., dish washing detergent, dish washer detergent, toilet paper, garbage bags, etc.). We found this strange, as we've never had to do this before and because the flat was not inexpensive in the first place. As well, the wifi did not work well.
Overall, we enjoyed our stay at Marc's place, but we thought it would have been excellent, had there been more attention to these details.