I have stayed in 5 airbnb's now and all but one had problems. Either smoking, not clean enough, no toilet paper, one guy even had a party while we were there and were making noise until 4am. Now I realize part of it is that I like my privacy, quiet time and things to be really clean so I gave airbnb another chance and rented an entire apartment. Everything was fine in this apartment until we flushed the toilet for the first time and a horrible sewer smell started to fill the air. The host was completely aware of the problem too when I emailed him about it.
Unless airbnb is the only way you can afford your trip it should be avoided at all costs.