@Aracely12 This is exactly the problem with charging extra per person, but there are some options that you can implement.
1) Be proactive and confirm the number of guests in advance-that way you can update the reservation to accurately reflect the number of guests.
2) If you notice after the stay you can send a message inquiring how many extra guests stayed the night and then put in a request for the payment through the resolution centre. You will want the communication between the guest and yourself to be on the platform so that you can involve Airbnb if the guest doesn’t want to pay.
3) Change your pricing structure, charge more per night and only add an additional charge after 4 guests (or whatever you think will work).
4) Lots if hosts have a camera doorbell and can therefore definitively know how many guests stayed. I suppose this is helpful to keep your guests honest if they know there is a doorbell camera.
I’ve tried quite a few different pricing structures and find that an additional charge per guest only works well if you are a home stay. Otherwise you are continually chasing down payments from guests and it becomes too time consuming.