Selling a course, and then honoring it
Most laser clinics sell courses because that is how the treatment works: a single session does not finish the job, and patients who pay per session tend to stop after three. Selling the course is the easy part. Keeping count of it across five months and three members of staff is where clinics lose money and goodwill at the same time.
A course is a number of sessions of one treatment, at one price, with an expiry if you want one. The count lives on the patient's record, so your front desk can answer "how many do I have left?" without opening a calendar. Raise your prices in March and everyone who bought a course in November still has exactly what they paid for, because the price was copied onto their purchase at the sale.
Patients can see the same number themselves on their own account page, alongside their next appointment. That is one fewer call your desk takes on a Monday.