We had a very nice stay at Siebe's flat. Siebe received us at our arrival, and explained everything about his flat. The flat is nicer than it looks on the pictures, and it's perfectly furbished and equiped for a short or long stay. TV, washer / dryer, full equiped kitchen, good bed, TV, and eveything very clean.
The flat is quiet, and very well located: close to the RAI for trade shows (10mn walking), close to metro and trams, and the local area is full of restaurants and bars. It's not really in the city super center, but with the new metro at RAI you can reach the center in 10mn walk + 10mn metro. Also, it's easy to park in the street.
I would strongly recommend Siebe's flat, and personnaly I would be really happy to enjoy it again when I'm back to Amsterdam.