You are correct. Airbnb states 'the higher the subtotal, the lower the percentage, so you can save when booking large reservations' but that's not strictly true, it's the opposite! The lower the subtotal, the lower the service fee. And the service fee is higher with a higher subtotal. Airbnb states the service fee covers things like 'if a host cancels', '24 hour telephone/email support' 'the running of the Airbnb platform'. But if you cancel a reservation in any case (unless it's for exceptional circumstances) the Airbnb service fee is non refundable. Hosts only pay a very small 3% fee when the guest checks out and they are covered by the £600,000 host guarantee.