Last time I used Airbnb, there was no adding people as a "+1" or anything. I booked a house with 5 beds and that was it. Airbnb would never know if it was just me or 15 of my closest friends. Has that changed?
Also, most airbnbs I’ve used have had a ring doorbell, and in one case a security camera pointed at the front door. The ring doorbell will alert them whenever there is motion at the front door, and they’ll be able to see who is coming into the property. There’s also usually clauses in their “terms and conditions” that state if you have more people than was booked well charge you extra blah blah.
Bottom line: if you run an Airbnb you’re going to make massive amounts of money and can essentially do whatever you want with it.