Maria met us when we arrived and showed us the ropes before going out. We didn't see her again after that, but her responses were very quick when we texted her a query about something.
The apartment is very warm thanks to the central heating and also very comfortable (apart from a few squeaky floors). There are takeaways and supermarkets in the neighbourhood so eating is never a problem.
The location is great too -- the 2A bus, which passes many of the important tourist attractions, stops close to the apartment. (But watch out for pickpockets preying on unsuspecting tourists using the bus.)
The washing machine/dryer are shared with other residents of the building and have to be booked in advance, which was a bit inconvenient because sometimes the best time slots are not available.
All in all I would say that Maria's apartment is an excellent choice for people intending to spend a few days in Amsterdam.