Conveniently changed number of guests on request after realizing additional fee

[Jeff238]

I have a guest who is 18 who sent an enquiry with 1 guest listed but in our conversation stated there would be 11 guests ages 17-19. I was immediately nervous due to the ages but proceeded to advise them that this is a family cottage that our young children adore and they must respect the property and the neighbours including no excessive noise outside and was ok with the booking. I advised her of the total price prior to sending the special offer. Which she originally agreed to. I sent the "Special Offer" upping the number of guests to 11 as she had stated (I have additional fee for any guests over 8 to a maximum of 12). Once seeing this and I'm sure she saw my "additional fee" note/function, she then tells me there will only be 8 guests. 

How do I get out of booking with her now in such a way that I'm not calling her a liar and that I am not discriminating for age? My main reason is for the assumed lie right off the bat.

Any help is appreciated.

[Daniel1843]

This has been a big problem for us.  Guests are allowing more people than they are booking.  We are including a stern warning with the checkin instructions to try and curb this problem.  We will have to see how that works for future bookings.   We just started to collect a deposit and are warning guests that we will charge them against their deposit if more guest arrive then booked.

[Letti0]

@Daniel1843  That's not going to happen on AirBnB the deposit they don't actually collect can only be used for damages.