@Richard146 Correct, I don't use Instant Book and never have. I do realize there are areas where there is such heavy competition that a host is at a serious disadvantage if they don't use IB. And I know that even the most experienced hosts who ask all the right questions, can be broadsided by a convincing liar. Some hosts have gotten pretty good, though, at asking questions that lead guests into a trap where their intentions become clear. Or making it clear that sneaking in extra guests, or whatever, will not be tolerated.
There's a bit of an art to stating things in a way that makes the guest understand that violating the rules will be to their disadvantage, and hosts who are good at that will often see the guests cancel as soon as they realize that getting away with their nefarious plans won't be an option.
Regarding IB, I also think a host has to weigh getting more bookings against the type of bookings they are getting. If a guest pays for 1, but the host ends up paying for the extra utilities, amenities, all the towels and sheets having to be washed, not to mention more wear and tear on the house, and likely extra cleaning time, because 5 people actually stayed, how financially advantageous is it to get more bookings? If it only happens once in a blue moon, it's probably no big deal, but if it happens a lot, it's something to consider.
Certainly the revenge review if you call a guest out on bad behavior, or charge them for damages is an ongoing problem, and one discussed ubiquitously on this forum.