I used to work at the front desk of an hotel.
More often than not if we tell you we're fully booked when you try to make a reservation, we actually are.
Buuuut.... Sometimes it's just b******t we make up because we got a bad vibe from you.
We get blamed if we accept a booking from a person who then trashed the room, or was just all around annoying/rude to the staff.
It's not all hotels I worked at that do this, but some do.