Cancellation by the renter: the refund
Cancelling within a short time of paying entitles you to a full refund, under the cancellation policy. The full details are on the cancellation policy page, /legal/cancellation.
The rental starts the moment the payment goes through. If your plans have changed, cancel from your rentals page as early as you can.
The amount shown on the booking is everything the renter pays. Nothing is added on top of it, so there is no add-on to hold back from a refund.
The refund goes back to the card you paid with. When it appears on your statement depends on the card company.