There is nothing more frustrating than a client who doesn’t show up for their an appointment. Most spas hold the client’s reservation with a credit card. If the client doesn't cancel their appointment, they are charged for it. Most private practice owners only accept cash, so they are even more vulnerable.
If you cannot make it to your appointment, please have the common courtesy to cancel it. That way, you will not be charged for the service and the spa or private practice owner can reschedule another client in your time slot.