The dynamics are such that bad reviews are rarely given by host or guest. The flow is carefully tailored to produce this result. As a guest especially, why complain about a place you’ll never revisit when the payback could be a negative review of you that makes it more difficult to use the service?
As mentioned by another comment, both host and guest submit their review before seeing the other's review. And they rarely interact again. Having looked at many property listings, and stayed at places with marginal reviews, I'm quite sure bad hosts get bad reviews. And I am pretty sure the same is true of guests.
Furthermore, guests and hosts submit a review a very high fraction of stays, and one cannot submit a review without actually hosting or actually spending substantial money as a guest, so AirBnN avoids most of the problems that Amazon reviews have.
You could make the same argument about Couchsurfing.
But actually, on Airbnb you can't see the review of the other person before both have submitted their review. That ensures that neither party retaliates.
