I've used Airbnb many times. Like it because you can find decent places to stay at hostel prices. For the most part Airbnb is quite helpful. Once the host had no wifi despite saying on their listing they did. Airbnb gave me $50 USD to go buy a data plan for my phone and I picked up a 6GB plan. No idea if Airbnb took that money out of the Host's money but it certainly did the trick.
Though I will admit I had one nasty encounter with a seemingly nice couple in eastern europe. Had great reviews and seemed nice but when we arrived they had left a msg they were out and left a key. Weird decorations, lots of anti-american stuff around too... We were sitting on the couch when the guy of the couple walks in and starts yelling at us, clearly drunk. I was with my sister at the time and it seemed like he was gonna get physical, so when he left for a minute we high-tailed it out of there. Ended up checking into a hotel at a not-so-cheap rate. Airbnb called us up and said that not only would they refund but they would pay all the costs for hotel as well. Gotta hand it to them for that and so I keep using them.
We actually never left a review for them, and I must point out though they are still actively hosting...