@Sam3811 You can't ward off a bad review from guests like this by refunding them in full or kowtowing to any of their demands. These kinds of guests will always leave bad reviews, even if you bend over backwards to accommodate their entitlement.
If a guest like this tries to phone you, do not engage in a phone or texting conversation with them. Tell them you only communicate through the Airbnb platform. An extortion threat by phone can't be proven- an Airbnb message can.
And with an abusive guest like this, get ahead of the game by reporting them immediately to Airbnb, and sending them a message like "XX- We were shocked by your rude and abusive phone call today extorting us for a refund in exchange for not leaving a bad review. There are Airbnb protocols to follow if you wish to cancel a booking and screaming at a host over the phone isn't one of them."