This has been a huge problem, All Airbnb can do is tell me to manually and physically requests for money. It ends up going back and forth and then explaining, and the guest will tell you they stayed somewhere else and they didnt have to pay extra, it ends up going back and forth and then you get a bad 2 star review and a warning from Airbnb that your listing will be suspended.
My 2 room apartment can sleep upto 6 guests. Most often than not, the guest never book the correct number of guest. I have a security camera that sees how many number of guests came in and spend the night. I have ask Airbnb to provide the possibility of changing the number of guest once they check in. They have said you cant do that. It is only at that moment that you can know how many are checking in. I dont feel like charging 6 guests thesame fees as 1 guests.
So what do we do? Almost nothing...