You don't have to approve every booking you received from the clients. If you had a bad experience with the client, you can simply decline his booking request. Or you can also cancel an already confirmed booking. It takes just a few seconds!
Bookings can be canceled in the booking details form (see chapter Calendar settings for more info) - just click on the booking directly in your calendar that you want to cancel.
In the lower right corner of the table, you will see the Delete option.
By clicking on it Reservio asks you if you want to cancel the booking. Either decline this option or confirm it by clicking on the red Delete button. If the client left his email, the system gives you an option to send him a message with the explanation (for instance, that you won't be available ;-))