Airbnb almost always favours guests in any dispute.
A guest need only claim that the place was filthy or had no water or electricity, and demand a full refund, and they're likely to get it, without producing one shred of evidence.
Hosts, on the other hand, can produce volumes of irrefutable evidence of a guest in violation of numerous breaches, including violations of house rules, parties, damage, and/or more persons than booked, and still risk being turned down for compensation by Airbnb.
That's just the way it is. It's been going on for a long time, and isn't likely to change.
Unfortunately, your only chance is to pre-screen potential guests extensively, before they book, whenever you don't feel comfortable with their request or inquiry - particularly when they have no profile or positive history. It's still no guarantee, but in practice, it greatly reduces occurrences like these.
No, it's not fair, but it's the nature of the beast.
