Every time I rented form Hertz the counter sales rep attempted to up-sell me. I quickly got on, and pre paid for my rental. When they try and up sell, I just tell them all I want is the car I've all ready paid for and I want it NOW. Works every time. Yes, Hertz no longer the number 1 company it once was.
The last two times I've rented cars, I've experienced a variation of that. I prefer full-sized cars, so I reserved cars in the "premium" category. Since they couldn't upsell me, they they tried to downgrade me at a premium price. They offered me Nissan Altimas. No way that's a premium car, and I also had to argue that I wanted the type of car I'd paid for. In the first case, the agent responded that the Altima was a premium car. I told him that I was a car guy who'd subscribed to four different car magazines for forty years and belonged to three different car clubs, I knew my cars, and that the Altima was far from "premium". I got my full-sized car.
The second time was different. I'd reserved my premium car using my AARP discount. When I got to the counter, they told me that because I'd gotten "a deal" through AARP, I didn't deserve a full sized car and should take an Altima instead. I held my ground, and ended up with a Mercury Marquis (sadly, without the coveted De Sade option). That was 13 years ago, and I haven't rented a car since.