Special Prices 
SAP Business One enables you to define special prices for your customers and vendors in addition to the standard price lists. You can define these special prices for specific business partners or by discount groups according to item groups, properties, or manufacturers.
When you process a sales or purchasing document, SAP Business One checks the following elements to determine the item prices in the document:
Are there special prices defined for the business partner?
Are there discount groups linked to the business partner?
Are there period and volume discounts defined for the price list that is linked to the business partner?
Which price list is linked to the partner?