1) You MUST put down a CREDIT CARD. Not a bank card, not a debit card, not a prepaid card. No plasticky no rentee. A major credit card to make a transaction. No bitcoin, no cash, no BS. Airbnb then puts a hold equal to transaction cost + 20% for the duration of the stay. That 20% can be put toward insurance on both ends, paid out when satisfactory closeout of the transaction on both ends occurs. If renters balk at the 20% hold, they shouldn't be on vacation. If owners balk at the "hold" instead of cash in hand, they can take their business to craigslist or wherever.
2) AirBnB must then become an arbitrator, a mediator, a guarantor, and/or (unless they want to outsource this) an insurer.