Plans change, and the earlier you cancel, the better. Each operator sets a cancellation policy for each kind of thing they sell: how long you get a full refund, and how much comes back after that. You see it with exact dates before you pay, and it is printed on your quote and invoice. Nothing comes back on the day of the trip or for a no-show.
If you don't cancel and don't turn up, the operator keeps the payment for the service. A security deposit on a hire car is still returned to you, because it was never part of the price.
Running late rather than not coming? Message the operator from your booking page. Most will hold a room or a pickup if they know.
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