@Toni173 Third party bookings are against Airbnb's terms of service. If the person who books is not one of the people who stays, you will not be covered for anything should you have a problem with the guest. Don't accept this- call Airbnb to cancel it for you on the grounds that it's a third party booking, and let the guest know that you have to do this, as it's against the TOS.
I know you're anxious to get your first booking, but this is not the way to start out. More bookings will come, be patient.
The guest's finances are his problem, not yours. He can call airbnb to question and complain about the discrepancy in price if he so chooses.