Cabcharge is also a private voucher scheme, nothing to do with credit cards (companies can give vouchers to people to use for cabs, e.g. QF can give distressed cabs a Cabcharge voucher for their taxi to/from the airport) ... the 10% fee was originally to cover the cost of that processing. I have dim memories that originally no credit cards were accepted, that is a later addition and the 10% fee was for risk (as this predated having POS terminals in the cab).