R30 shipping misleading

They advertice shipping R30 on all items. Im a seller for many years now buyers pay R30 to R80 but if a parcel works out R300 then the seller must pay out of there pocket. They already take success fees but now with the new shipment terms sellers lose lots of money, its not fair at all. . This is not acceptable to me. I prefer the old bid or buy. This R30 shipping is misleading for me