The same thing happened to me. The guest came with extra guests that had not been approved. She had booked for four, and I had confirmed with her the number. She came with 7 guests. I let her know the were not approved, and she said, "well, seven people are coming anyway." She then caused a lot of damage and expenses for me, due to the 7 guests.
I pursued a request for extra guests fees, since she had brought unapproved guests, and my listing contains a fee for additional guests. It was a long, drawn-out process, badly handled and mismanaged by AirBnb, to say the least, with each customer support person giving a different version of the policy.
In the end, one case manager asked her to pay half of the expense (I had already compromised down from what my listing fees indicated was the extra guest fee). She said she would, but only if I took down the review I had posted, that said many positive things, but I also said that she brought extra guests. I declined to remove the review, because it accurately reflected my experience. However, after I declined, she then asked AirBnb to remove her positive review of me. They deleted it.
They claim they have a policy against extortion, but they do not. She wrote a review before seeing mine. Once she saw my review, she offered to pay for damages only if I were to remove my review. When I did not remove my review, she removed hers.
This undermines the whole transparency of the AirBnb review process. The community is based on honesty and transparency in reviews. When someone is allowed to engage in "tit-for-tat" behavior, it means that I am pressured to not post an honest review on the guest. In this case, I did not cave, but it was because I believe other hosts have the right to know that this person was rude, entitled, and never once even apologized when I messaged her individually to let her know that it was not okay that she brought 7 guests. The system has no credibility, since they allow guests to seek revenge by removing their own review, and this is against their own publicly stated policy.