This is from a recent prolonged discussion I've had with Airbnb:
"The issue is complicated because there's a difference between unauthorized guests, and unauthorized visitors.
Unauthorized guests are people that stay overnight. That is not allowed according to our terms.
Unauthorized visitors, are people that enters the listing for a certain period but don't stay overnight. They are not considered guests.
This is where things get confusing, because we don't have an specific rule for visitors on our terms, we only have for guests."
Despite 2.3 of the Terms of Service stating:
"2.3 Accommodation Reservations. An Accommodation reservation is a limited license to enter, occupy and use the Accommodation. The Host retains the right to re-enter the Accommodation during your stay, to the extent: (i) it is reasonably necessary, (ii) permitted by your contract with the Host, and (iii) consistent with applicable law. If you stay past checkout, the Host has the right to make you leave in a manner consistent with applicable law, including by imposing reasonable overstay penalties. You may not exceed the maximum number of allowed Guests."
And Airbnb previously stating:
"Allowed guests" means the number of guest registered in the reservation.
In case a guest books a reservation for 3 people. Only 3 people are allowed in the listing, unless the guest contacts you and ask if you would authorize an additional guest. If you authorize, in this case, it's OK to bring an additional guest."
In essence, Airbnb seems to make up the rules as it goes along. The Terms of Service are quite clear and refer to "Hosts", "Guests" and "Members", the term "Visitors" is nowhere to be seen and even though Airbnb confirmed in writing that "Allowed guests" means those on the reservation, this was later retracted.
So now it seems that if they don't stay over, they are visitors and you can charge if it's in your House Rules, but the Terms of Service make no provision for this charge, only the "Extra Guest Charge" is covered. I have a terrible feeling that when it comes down to it, any attempt to charge for "Visitors" will be refused by Airbnb on the basis that it's a violation of the Terms of Service.