If you know more people are using your property than have booked you have two choices
1. ask the guest to send an amendment to the booking for the additional guests
2 . If you don't have room or don't want the visitors to stay then tell visitors not on the booking to leave immediately
do you ask all your guests to confirm on Airbnb messaging to confirm numbers of guests that will be staying and that they understand only guests who have booked can stay @Gavin238
(I am presuming you have set up your listing so there is a per person charge for any additional guests over one)