A client can book but can only cancel one of their appointments if you flag that client as "trusted".
Your trusted clients will understand that they cannot book alternate times and dates because
neither you nor your other online clients would be able to use that second time slot.
All non-flagged clients will be responsible to you, the owner, for their online bookings.
To cancel an appointment those clients can either send you an email or call you directly to request a cancellation.
By default only you and your assigned managers can cancel appointments. When cancelled, that time slot in the appointment book will be cleared and the person who booked the appointment will receive a cancellation notice.
If a client has booked the appointment it will be marked CANCELLED and moved to the past section of their PAC.
