You may set a discount for your frequent clients on selected items:
First enable discounts in Settings > General > Department settings >Show discount on client
Then set the discount by going to Clients&Patients and then search by name. When you find your client, click on their name to open up their file. Scroll down to the end of the screen to find Client Discounts and select +Add.
Set the items you want to give a discount from and add the %.
The discount % will be automatically added to the client’s items which were specified for the discount.