Why is it more expensive for a Preferred member?

Good day I recently went online to make a booking for a car in CT for 3 days. When i tried to make a booking with my Wizard number, the quote i got back was 30% more than when not using my Avis preferred number. Surely as a preferred member I should not be paying 30% more than when I am not a Wizard member. Please can you explain to me why there is such a significant difference in the quote? <br> Thank you