Turnover charge

I understand the turnover charge on NSW racing is a necessity in order for Betfair to operate on NSW racing but they are blatantly ripping customers off with their calculation of it. They assume a 3% implied commission on losing bets, when it is a 10% commission market and a minimum 7% commission when considering discount rate. This means losing bets are treated far harsher when calculating the turnover charge. How is this allowed to happen and what can we do to change this?