Customer screen > Account Details tab
Use this button so that the selected customer can receive a special cost price and/or special selling price.
1.Click Add to add a new product.
2.Use the product details screen to search for a product and click Select Product.
3.A new row is added showing product code, description, manufacturer and price.
4. a) The price shows the normal selling price and cost price
b) Over type the price with a new price
c) Tick the Use box
You can alter either the cost or the selling price, or both.
5.Repeat as needed.
6.Click 
Update to save and close.
If you need to specify more than 1 type of discount you need to know the order in which they are applied. There is a hierarchy where one discount overrides the other.
The order goes from least specific to most specific:
•Product Discount •Discount Band •Catalogue Discount •Product Prices |