Hi all,
I use the following rule: if a guest (account holder) informs me before actually making the reservation with explanation of who is coming (e.g. family member, close friend, part of a present) I will accept. The key point is that the account holder is frank and straight forward about it.
If the account holder informs after making the reservation, I would rather be inclined to not accept and ask Airbnb to cancel without penalties, which is not a problem as the account holder violated the Terms of Service. Obviously, if the explanation is acceptable, I might proceed with the reservation.
When it comes to guarantee from Airbnb in case of problems, property damage, excessive cleanliness issues after check-out, review disputes, etc. the account holder is still the final responsible person. Nevertheless, have in mind that, often depending on the CS agent, you may not be covered by the Host Guarantee Program.
I agree that the mayority of the guests behave much better as they are aware that they are enjoying a present, or courtesy, of a member of the Airbnb community.