@Robbie54
If you worry about bad reviews you'll never be able to manage guests out to take advantage of hosts.
With that in mind, I suggest you get outdoor surveillance.
All you need is photos showing no. of guests that entered your home and a request for payment - also make sure your security deposit is enough and include in your house rules that it is the guest's responsibility to book and inform host of accurate guest headcount. Keep messages short and business-like. Request money, give them 24hrs to pay and if they don't accept, contact ABB to charge them from the security deposit.
This is one area where ABB is known to actually take the host's side as long as you can provide photo-evidence.
Also, if it were me......I'd give that guest 1 stars all around and a simple "My experience hosting GUEST and group was uncomfortable. I would not welcome them back."
Good luck~