Cannot accommodate a room change - sold out

This happened maybe a couple of hours ago. Checked in a guest, but immediately after check in they report that the room smells like smoke. (Entire facility non-smoking btw, but still doesn’t stop people from smoking anyways)

Can’t initiate a room change due to the hotel being fully booked for the day. We still have some remaining arrivals, but still can’t do a room change.

And the guest is adamant that I do a room change. Because I checked them in to a “smoking room”. The best I could offer is to have a houseman spray down the room. But they still wanted a room change, and an email stating that I’m declining their request (nope).

The manager is out of office, and of course they want to talk to the manager. I called the manager and asked what she wanted to do, and it was to the same effect of, we can’t move them, we’re sold out. We could offer a discount because of the inconvenience, but you guessed it, it’s a third party reservation.

For the time being, they left the hotel to take in the sights. I made sure to check the room myself, and wouldn’t you know, the room DOES NOT smell like smoke, but the bathroom had been used by the guest. And I definitely cannot do a room change because our housekeepers are gone for the day. The available houseman speculated that the guest blew up the toilet, but the bathroom smelled just fine.

So, kind of just waiting for the guests to return, only to inform them that a room change will not be possible. I already had the houseman spray down the room.

Humbly asking fellow FDA on how to approach this professionally and graciously because asking for a written email from FD seems like too much.