I also had a flat where I got a letter sent to my next address the afternoon I was moving out. saying the inspection had found damage and the necessity for professional cleaning. I was in when the 'inspection' was supposed to have happened. on another I kept a key until the last day and they claimed to have inspected but the pile of unmoved mail proved the door hadn't been open for weeks. It is definitely seen by some agents as a post tenancy payment. some agentsdon't tell the landlord they have done things like this too..