S.C. Code Regs. § § 103-198
Unless otherwise specifically exempted by the commission, no motor carrier operating under a Certificate of PC&N shall charge, demand, collect, or receive, or cause or permit its agent, servants, or employees to charge, demand, collect, or receive a greater or lesser or different compensation for transportation, or for any service rendered, than the rates, fares, and charges specified in the lawfully applicable tariffs or schedules in effect from time to time; and no motor carrier shall refund or remit in any manner or by any device, directly or indirectly, any portion of the rates, fares, or charges so specified, or extend to any person any privileges, facilities, or services, or do or perform any service, or give, remit, or refund anything of value except in accordance with said lawful tariffs and schedules, or specific order by the commission.
S.C. Code Regs. § 103-198