@Bronwen3 I just have all the beds made up, for each reservation. One is a pull-out bed, so I only have that ready if I have four guests (my maximum).
I had it happen, one time, that someone booked for one, which travelling in a group of four. I didn't find that out until day of check-in, where he said the other folks "weren't going to stay the night, but just shower and change" before catching their flight out. Which, to me, is using the amenities, and so I charged them the extra fee.
As it happened, their flight was cancelled due to weather, so they all spent the night, anyway, and I didn't have to rush in and make up extra beds.