When we arrived, there were a few issues with the flat. Most obviously, the smoke alarm had been tampered with. It was hanging open and missing a battery. Less obvious was the source of the damp/smoky smell. We identified the badly stained area rug as the cause of the unpleasantness after my socks got wet from walking over the rug. We rolled up the rug and put it on the balcony for the evening. We also mopped the area where the rug had been, as it was wet and sticky.
We also found an unknown gooey substance on the bedside table.
We asked to be reimbursed for the cleaning fee as we felt that these issues should have been resolved or raised by the cleaners. However, the host decided not to waive the fee. They also waited until after we left to address the issue with the smoke alarm.