Since a lot of this is chatter about booking with Amex and paying with another card, hoping my question isn't too far off the topic... When booking with the Amex Platinum card, you qualify for some very specific corporate discounts (I only rent about once a year, but I keep getting BMW and Mercedes rentals for the price of a midsize) and the fine print says that you must actually pay with the Amex Platinum card to get those rates. Has anyone had success in keeping those rates when changing payment methods?