Coupon sites are not allowed on the program.
Commission is paid on the net price of a sale (ie sale price before taxes). This means for UK and EU orders, commission will be paid on the net price (which excludes 20% VAT). For example, on a £100 sale the VAT (government value added tax) is £16.67, so you will be paid the commission on the sale amount of £83.33. There is no VAT on US sales, so you will receive the commission on the full amount of the sale amount for these orders. Eg for a $100 sale, you will receive the commission on the full $100.