For the last few years I've used the "Virgin Guest Rate PH" CDP, and before that I would use QF or NRMA discounts offered by Hertz, and they were always added by Hertz representatives when making phone bookings, and they always told me the best one to use, depending on where I was renting.
When I called Hertz this morning I told them I'd heard that there is a discount of 15% for Amex Platinum Charge cardholders and I gave the lady I spoke to one of my booking confirmation numbers. She said that the discount for my booking would actually be 20% and changed it from the 5% Virgin Guest Rate that had already been applied to my booking when it was booked through their call centre late last year. She then changed my other two bookings to the Amex Platinum discount as well.
I have not seen any information on any of these discounts on the Hertz website - I have relied on the Hertz staff members to tell my I am entitled to use them and they have then applied them to my bookings. For my bookings in the USA and Canada there has been no excess on the Loss Damage Waiver which is included in the rates I have paid.
I have not read of any change to the excess amounts when using the discounts so I'm wondering, after reading some of the posts here, if there could be a problem using the discounts that I am told by Hertz that I am entitled to since I do have an Amex Platinum Charge card, and that card is registered as my primary card in my Hertz Number One Club Profile, with my Platinum Reserve card registered an additional card on the account.