My wonderful scenario of the night:
~7:15p: notification that the front door has not been locked for 5 minutes.
~7:18p: Ring doorbell goes off; I see guest A who has left the door unlocked, enter and talk on cell phone; about 20 seconds in, two people enter from outside, who are not guests.
~7:20p: Neighborhood Watch texts to say that people who hang out on the block seem to have entered the front door (there is a problem with teenagers and others hanging out on property owners' porches when they are out, etc).
~7:20p-7:45p: I review video and try to figure things out, messaging all parties; I see a pair of Irish undergrads who are staying in a large bedroom upstairs, handing out on porch with local teenagers; the latter are sitting over the stone eaves; one is smoking and it doesn't seem to be tobacco *(I'm mean, not necessary a big deal but given circumstances...) ; the same woman was on the entry video.
~7:50p: I've sent several messages to the Irish students and called 3 times; I can see them on the front porch cam, and the guy is looking at his phone. I call the Superhost line...
~8pm: I'm on the line when I get a message from Irish guy that there must have been a misunderstanding, the people were people they work with; while I'm on the line with SuperHost support. Support says that if they're leaving, they'll call and warn them that if they have unauthorized visitors again, ABB will cancel at their cost.
~8:05p: I see unauthorized guests leave.
Now-- for now, I'll leave this to work out for yourself; I've read over the other "sneaking in extra guests" threads. How you handle it is one thing; but I don't see, at least in a shared environment with potential liabiities that abound, how you can allow anyone not on the reservation in the property except with advance notice and many questions-- what if they steal from other guests, for instance?
If you've just allowed them to waltz in...
FWIW: my other question here, is what would you do (WWYD?) in such circumstances; (I'll have more of these scenarios in the future, of course!).
Happy Hosting, or at least-- may you avoid Unhappy Hosting.