In some cases, as a service provider, you want to apply a discount to a specific client from the entire pricelist. You are able to do this by doing some configuration in your client's profile.
For example, if you want to apply a 10% discount to an entire pricelist for a specific customer:
Go to Service > Manage Clients > Select Specific Client > Account > Service Terms > New terms > Payment Terms > Discount > Approve and Update