But it can also be:

1.) get "illegal" money from somewhere/anywhere. Create bank accounts under fake names with the "illegal" cash.

2.) host receives payment minus AirBnB fees 2 days later

3.) host transfers amount minus his own cut to criminals

4.) AirBnB never gets notified of anything - it's just another happy customer.

So the problem with this scenario is AirBnB never knows about the problem - so all the "bad" hosts can go on for long times, and you dont need as many accounts; thats where the "scalability" comes in.