The house in Berkeley turned out to be a hovel!
Having confirmed my reservation for a room in a house, the owner then emailed a few hours later to say it was no longer available and there was only a mattress in the living room. I really had no choice at that point, so I accepted for a (slightly) reduced rate.
The owner wasn't there when I arrived, but his flatmate let me in. The room was filthy: dirty wall-to-wall carpet, bicycles parked on one side, empty pizza boxes on the floor. I was shown the couch, which looked as dirty as the floor, which had several blankets on it but no sheets. I took a look in the kitchen and found the counter tops strewn with unwashed cooking pots and pans, the sink piled high with dishes. The bathroom was as bad, and the shower cubicle clearly hadn't seen a squirt of Jif for years.
The flatmate called someone to come and prepare the room while I went out to dinner. When I got back there was a mattress with sheets, though I couldn't tell how clean they were. I used my shirt as a pillowcase and slept in another one. I also wore my jeans to bed.
This morning I couldn't find fresh towels so I used the cleanest looking white one I could find hanging up. I put another towel on the floor of the shower cubicle in the hope that whatever bacteria lived on it were less offensive than the community that inhabited the mouldy cracks in the tiled floor.
Needless to say I'll be leaving a review on Airbnb. It will probably be a copy-and-paste of the above.