Thanks for your response Andrew.
Yes, the second bedroom is now furnished but there has been no suitable gap between guests to do new photos. Yesterday's guest booked in the knowledge that they had not seen up to date snaps, as have a number of previous and future guests.
The photo of the empty room was to show the size, really.
You say that "no one in their right mind" would choose the apartment, but we have plenty of enquiries and bookings. So either we are getting contact from people who are out of their minds, or people who are quite happy with our ad!
Pre-Air BnB we never had any complaints about stock photos, providing the accommodation was as good or better than the photos. Hotels rarely show a photo of the exact room a guest will stay in. The law in the UK for guests in serviced apartments almost requires that a guest is not hiring a specific apartment. I won't bore you with the details unless you would particularly like me to.
As for meeting guest in person, unfortunately I don't have staff to meet people at midnight, 3am etc. which is what guests require often. But I would expect anyone of average intelligence to be able to go a building, open the key safe and locate the second floor.
Whatever the rights and wrongs of our advert, though, if a guest turns up and says there is no furniture I would expect them or Air BnB to contact me to ask what is going on. There was no attempt at contact from either of them.
I am going to go over to the property later to check that no one has emptied it of furniture. My best guess remains, however, that the guest has either not been to the apartment at all or otherwise somehow managed to access an empty unit on a floor other than the one they were directed to.