I know you used to be able to call Hertz and have them set a "do not upgrade" flag on your account. Maybe still true? Give them a call...I know back in the day it was not on the website. You had to call them.

Right when they launched Prestige Collection (2000-ish), they were giving all sorts of nice upgrades out to promote the new cars. I was renting cars on client trips...it crossed my mind to have the flag set on my account so I didn't get something *too* nice. Sort of hard to roll up to a client's office in a Jaguar...

Alas, those upgrades were short-lived and I'm no longer "concerned" that Hertz will put a Jag in my stall.