I have used Airbnb over 15 times over the past two years, and this is was my first bad experience.
The main issue was that the communication and the relationship with the hosts, Brian and Rachel who live upstairs, was not good and at several points we had unpleasant situations. This was in part my fault because I had a last minute request for extra guests that was not clear. Brian and Rachel kindly agreed to allow the extra guests for an additional fee, which was very kind, but then became very anxious about the money and sent a series of strongly worded messages that made me feel very uncomfortable. Similarly, shortly before checkout on the last day it started to rain and I asked if it was at all possible to delay check-out a few hours, and then received a reply saying that the fact that I couldn't bother to ask this earlier was unacceptable and that they needed me out of the property at 12h00 sharp. There were other situations like this during the say.
Minor issues: the fridge was not cleaned properly and there were traces of food from the previous guests. There is no kitchen and this was uncomfortable because I could not cook and had to use disposable silverware. Also, the wifi connection does not work properly.