Certain types of patients need a "hard" confirm, such as:
a. Patients who have previously broken an appointment.
b. Patients in their 20s (older people are usually more reliable about keeping doctor appointments).
c. Patients who use Medicaid or any other government plan.
d. Patients who have not been in for some time except for an emergency.
e. International patients as there may be language barriers or different cultural moral codes.
f. Parents making an appointment for their grown child, or a spouse making an appointment for a spouse.
If you can't get a hard confirm on these types of patients, consider double booking.