This kind of thing isn't unique to Airbnb. I believe any online marketplace (eg eBay etc), has similar problems.

My usual approach is to keep as much communication on the platform as possible, including the payment process. Anyone who tries to communicate off the platform (eg send money via another method) immediately warrants more scrutiny.

In this case, there are probably things Airbnb can do to help users and reduce the likelihood - for example I don't see the host's email address until I've paid (via the site).