I never actually used Airbnb but I did use Couchsurfing a lot. One time I was in Sri Lanka, I decided to stay with a host who had hundreds of positive reviews. But the guy was actually charging for everything from food to the toilet paper (which is not really the spirit of Couchsurfing). I was more sad about the false advertising than the fact that I was charged for all of that and that the place was far from clean.