Per FCW article http://www.fcw.com/print/11_33/news/90256-1.html, it was determined during Sun's option to extend their GSA schedule for five-years that Sun had offered better discounts to some customers their GSA pricing.
First, this is clearly acceptable behavior and occurs everyday with any large corporation like Sun. Under the price monitoring clause of Sun's negotiated class(es) of customers in their Final Proposal Revision (Basis of Award), Sun is required to pass along any favorable pricing/concessions if the item is on their schedule and is sold during the same time as any GSA order. While Sun can and likely indicated in the CSP's for their renewal that they have deviated from their stated business practices, all they needed to provide is (1) a discussion of the situations that lead to deviations from standard practice, (2) an explanation of how often they occur, and (3) the controls you employ to assure the integrity of your pricing.