I booked on Saturday for a stay starting on Tuesday, got an automatic confirmation that day, and a follow-up non-automated confirmation on Monday, and then was told the day I was arriving that the place I booked wasn't available.
They offered an alternative place about 20 mins walk / 10 mins drive away, so wouldn't have left me totally stuck, but I picked this house (over others available on AirBNB around the village at the time) for the places and people it's in walking distance of, so that wasn't a good replacement, and I ended up putting off the trip.
The person I dealt with was perfectly pleasant throughout, and was ready to offer a refund when I said the alternative didn't work, but it was still a very frustrating experience.