I had a good experience in Cristina's house. My arrival was a bit accidental: the house has two storeys, and I didn't realize from the pictures in the web that part of one of them was being reformed. Since it had been some time since the apartment had been in use, the wifi wasn't working, and there was no hot water. However, Cristina is completely reachable via online, and there is an intermediary in Rotterdam to call if there is some problem. Therefore Cristina managed to solve all of my problems online in less than 24 hours.
The fact that part of the lower storey is being reformed didn't bother my stay there at all, because you do most of the living in the upper floor.
The location of the house is excellent, there is practically no need to take the public transport, since you can reach most of the interesting places in Rotterdam walking.
I communicated with Cristina by mail almost every week, and I could talk to her about any problem I had in the house, and she will give me a solution.
I would definitely come back if I should need to live for some time in Rotterdam.