Choose a commission basis and write it down
Common bases are a percentage of service revenue excluding VAT, a percentage above a monthly target, or a fixed amount per treatment. Whichever you choose, define it on net revenue after discounts and excluding VAT, and say whether package redemptions count at the redemption value or the price paid. Ambiguity here causes most staff disputes.
Worked example: a therapist earns 10% of service revenue above AED 8,000 of monthly net sales. In October she performs AED 14,600 of services, net of VAT. Commission is 10% of AED 6,600, or AED 660.