We got dinged with one that was our fault, but felt the punishment way out-weighed the crime.
We took on a handful of properties from a new client. They wanted to keep their old bookings though and leave them under the old PM to be sure the guest's wouldn't cancel when switching over to the new listing. So we had to manually block off the dates for about 80 reservations across a bunch of properties.
Well, we missed one and accidentally took a booking on our listing for dates that should have been blocked off. We noticed it pretty much immediately (within a few hours of booking). We reached out to the guest but they weren't willing to work with us on it, adamant that they should get to keep the booking.
We ended up having to pay the fine and had our listing penalized pretty heavily. It was our fault so it is what it is, but it sucks that an honest mistake that would have been a super tiny inconvenience for the guest ended up being a huge thing for us with a monetary fine and likely lots of money lost in future reservations.
Oh well, live and learn. At least we're a company with redundancies to make this happen very very rarely, and with enough inventory to make it not the end of the world. I really feel for regular owners. The whole point of Airbnb/VRBO is regular people are supposed to be able to rent their places, and those people make mistakes (especially on VRBO's garbage website). Punishment seems way too harsh on those folks.