The other reviewers are spot on about Mark and Sebastian's apartment! It was perfectly located out of the hustle and bustle of Amsterdam Centrum (~10 minute walk from Centraal Station), but a quick and easy walk to access many cool spots, including the popular Haarlemmerbuurt shopping area.
The hosts were very accommodating, as well as easy to communicate with and quick to respond. They thoughtfully left some wine and beer upon arrival, as well as a map of Amsterdam marked with some sightseeing tips. I got great sleep every night thanks to the peace & quiet and the very comfortable bed. It's worth noting that the bed is located in a loft area, but if stairs are not an issue for you, it's not a problem -- I did not find them to be that steep.
in short, this place is perfectly located and a great value. I would recommend it to anyone for their stay in Amsterdam!