Retailers finding their voice are among the new batch of submissions to the Financial System Inquiry.Interchange is the quarry of angry merchants sick at the level of bank fees and eager to rebate these charges to their customers.Spicing up interchange through "open transparent pricing in real time" is the aim of Marion Johnstone, group treasurer at CSR."Differential fee recharging by merchants," is her goal, one that banks and card schemes will no doubt say is difficult to adopt.Repco owner GPC Asia Pacific said merchant fees were "high and increasing" something blamed on their customer base's choice to wield premium cards on which acquiring banks earn better inter-bank fees.There is "rapid growth in co-branded American Express cards" John Moller, GPC's managing director, told the FSI.