Generally you can only recognize revenue when you are at risk for it. If you are not taking a risk by holding inventory (or guaranteeing a price before selling a service) then you are an agent, not a principal. You can only recognize the revenue that you are at risk for, the rest is "pass-through." This is addressed in the FASB ASC 605-45 (https://thegaappost.com/sec/605-revenue/605-45-principal-age...).
An example:
1) An advertising agency buys media for a client to place ads in, but their contract with the media company says they will only pay for the media if they are paid by their client. In this case they can only recognize their commissions and fees as revenue, not the cost of the media itself.
2) An ad network buys media for a client but has to pay the media company for it whether or not the advertiser pays them. They can generally recognize the cost of the media as revenue, along with their commissions and fees.
AirBnb does not take risk on the portion of the customers' payments that go to the host: if AirBnb is not paid then the host is not paid, so this part of the payment is not recognized as revenue.
An example: 1) An advertising agency buys media for a client to place ads in, but their contract with the media company says they will only pay for the media if they are paid by their client. In this case they can only recognize their commissions and fees as revenue, not the cost of the media itself. 2) An ad network buys media for a client but has to pay the media company for it whether or not the advertiser pays them. They can generally recognize the cost of the media as revenue, along with their commissions and fees.
AirBnb does not take risk on the portion of the customers' payments that go to the host: if AirBnb is not paid then the host is not paid, so this part of the payment is not recognized as revenue.