I had something like this come up just this past weekend for the first time, out of 200+ stays so far.
A young couple booked the place, they were getting married, and asked if was ok if a couple of people helped them get ready in the morning. It was fine, I told them I appreciated them asking. I DO have a strict no parties/events rule (as well as no fires, shoes on in the house, or leaving food out due to wildlife… I’ll get to that shortly), and the rental is just for half of the house, as the back half is still being slowly remodeled, which includes a porch.
I get a text from them in the afternoon asking if they can move things off the porch. I hurry on over there, and discover that they’ve set up for a wedding reception, it’s already decorated and everything. On the porch that is not included in the reservation, on the back end of the house. They said just a few people were coming over after the wedding. I didn’t want to ruin their wedding day, so I decided to let it slide and keep an eye on the situation although normally I’d shut that down immediately (the listing is a guest house, it’s literally in my backyard). Later I notice that a big wedding cake is sitting out on the porch, unattended, for about 6 hours. This is for a listing in the WOODS with lots of wildlife, including tons of black bears. Hence the no-leaving-food-out rule. I message them to ask if they want me to move the cake so a bear doesn’t get it, no response. Later that evening, their guests show up before them, bang on my door and demand to be let into the rental. I said no. It didn’t end up being a huge party, but still around 20 people, and they were also tromping in and out of the no-shoes house with muddy shoes, and had candles covering the timber framed porch. I was seriously unhappy with this, but again didn’t want to ruin their wedding day.
My solution was to let ABB know every single thing that was going on as it was happening, via their message app, so that if a serious problem arose it was well documented and action could be taken swiftly. They appreciated that I didn’t want to disrupt the guests’ wedding and were also completely and totally on my side, due to the way I addressed it.
In the morning, I messaged the guests, telling them I hoped they had a wonderful wedding day, and that I’ll be in touch re: the special event fee, since events are not permitted. I also told them that the fee would depend on the condition they left the place. They did indeed leave it in great shape, profusely apologized, and paid my request for an additional $150 immediately.
Moral of the story: Have things clearly outlined in your rules, contact ABB immediately as soon as you suspect there is a problem, and remind guests that you will be charging them extra if they trash the place. And if you are really nice about it all, they may even leave you a good review (my partiers did)