When a guest makes a booking, their reservation is confirmed immediately. Depending on your policies, a guest might be able to cancel their reservation.
If a guest contacts you in order to cancel their booking, advise them to do this through their confirmation email or Booking.com account. You can't cancel a reservation on their behalf.
The only cases where you can cancel a reservation are as follows:
Invalid credit card:
For information on what to do when the guest has an invalid credit card – read this article.
For help on what to do when you have an overbooking, contact the Customer Service Team.