Very poor customer service, but not all that surprising to me. I've rented at GSO the past two weeks, and they tried to "game" me both times. First time on a coupon, second time on gas. This is becoming more and more prevalent.
By the way, Hertz typically begins weekend rentals at noon on Thursday. However, whatever rate came up on Hertz.com should've been honored, no questions asked. The clerk's comments to you were total BS.