@Anonymous
Airbnb Terms of Service make it quite clear that it's not acceptable to bring additional guests, but I agree that there are guests of a certain type who will try to take advantage of a hosts softer nature or negotiate their way around the rules.
From a host perspective, I am always concerned that should something happen, in particular, should the "extra" guest have an accident or cause some damage, then Airbnb could simply walk away because there's no valid reservation covering the extra guest. Certainly where I am, it's illegal to have people in the accommodation without a reservation so if something happens not related to the host and accommodation, but it comes to the attention of the police that the "extra" guest isn't on the reservation then that's another potential "complication".
Having had any number of this type of guest, these being the very people that don't care if the host loses his tourist licence because if their actions, and therefore they don't care if the next lot of guests have thier holiday ruined because of this, I am afraid I don't play their game.
I am sure there will be some who might judge me harshly, but I evict them without exception, this type of guest has no right to expose me to criminal proceedings, they have no right to jeopordize the reservations of the guests that follow them and, of coure, they have no right to steal from me which they do when they use facilities that they haven't paid for.
There can be very, very few excuses for turning up with more guests than appear on the reservation and even fewer excuses for not even extending the common courtesy of talking to the host prior to check-in.
Amazingly most of them manage to look quite hurt at the eviction. Makes for good Instagram posts.
I had one guest the year before last whom I evicted, within a couple of hours she'd posted that she'd been evicted (again) from "the Airbnb" adding it wasn't the first and she didn't expect it would be the last time this happened.
Sums up their little game really.