@Lorren0 I don't have experience with cameras, but I do have experience with guests who will use every excuse in the book to get a discount.
Your best recourse is to make sure that you communicate with the guest via the Airbnb site, so there is documentation. Even if they text you. If they text or call you, then type up the conversation as best as you can recall in a "just to confirm our conversation" Airbnb site entry.
"Per our conversation about the security cameras - they are noted in the description of our listing. They are there for your safety and our protection. Also described in our listing are the areas that are off limits to guests, located behind locked doors."
"It has been mentioned by our neighbors that they have witnessed more than 2 guests on the premises. Your reservation specifically stated 2 guests. I have submitted a reservation modification reflecting this change."
"I'm sorry you feel you've been misled, but all this information is included in the description."
Also, it is not illegal to have security cameras on your property in California, or in your home as long as their location does not intrude where there is reasonable expectation of privacy. This would be rooms such as bedrooms and bathrooms.
AND, reviews go both ways. When it comes time to reviewing these guests, make sure you do NOT recommend (thumbs down!), and explain why. While a bad review is hard to get rid of, you can respond to their review on your page. If all of this is documented on the Airbnb site, then Airbnb might side with you and erase the review.
I also agree with @Helen3 about contacting airbnb re the threat of a bad review.
Hope this helps, and good luck.