Special Prices 
SAP Business One lets you 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, manufacturers, or items.
You can define special prices only in one currency, based on one of the item's prices (each item can have up to three unit prices with different currencies). In addition, you can set different special prices for each unit of measurement (UoM) of the item.
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?