My wife and I, along with another couple, stayed at Martina's place for 10 nights over the Kingsday Holiday. I echo many of the points in the other reviews. The apartment is clean, spacious, and in a location that can't be beat. Right near the Waterlooplein Market, most of the attractions one would want to see in Amsterdam are less than a 20 minute walk. It's very close to any amenities one may need, including supermarkets, restaurants, and even a charming old bar right next door.
Martina was a good host. Hands off, but always quick to communicate when we had any questions. Our flight came in quite early the day we arrived, and she was gracious enough to meet that morning so we could drop our luggage off. Her cat Joepy was a nice addition. He's a sweet cat who loves to sit on laps, but is also content to be left alone.
I would recommend this place to anyone visiting Amsterdam who wants to be in the centre of it all. If I ever return with another couple, I would definitely consider Martina's place again.