AirBnb seem to have a different policy now: they simply delete the bad reviews. In June I had my first bad experience. The owner was nice but the property was absolutely awful (yet it was a "superhost" with glowing reviews).
I left a bad review (my first). Two days later I received a convoluted message from support, telling me that my review was incorrect and wouldn't be published, because it pointed out "things the property owner couldn't change".
This is sinister, but funny at the same time. If the property is dirty it can be cleaned. But if, for example, it has walls so thin you can hear the neighbors breathing, or the slope of the bathroom is in the wrong direction and water flows into the bedroom every time one takes a shower, you can't say that in a review! Because it "can't be changed".
I learned from that experience that AirBnb reviews can't be trusted, and "superhost" doesn't mean anything (except the power to kill bad reviews).
I haven't been to an AirBnb since; the best properties are very often on Booking.com as well, and those which aren't, are questionable.