You can add contract discount on services for contract quotes and service contracts. The discounts can be on spare parts in particular service item groups, on resource hours for resources in particular resource groups and on particular service cost.
Open the 
Service Contract Quote window.
Browse to the contract quote to which you want to add discounts and click Contract, Service Discounts. The Contract Discounts window appears.
Press F3 to enter a new contract discount.
Fill in the fields in the Contract Discounts window. For Help about a specific field, click the field and press F1.
Repeat steps 2 to 4 for each service discount you want to add to the selected contract quote.
Creating Service Contract Quotes