Even if someone higher up at Hertz had a devious plan to install these cameras into every vehicle and covertly film all their customers, there is no way in hell that any rental car company I know of could implement such a system. Most of the time they can barely get you the car you supposedly booked for the price you were quoted.
I've never had a problem getting the rate I was quoted. It's common that they are out of the particular car class I ordered, but that's to be expected, they don't have unlimited room to store each of a dozen car classes. They've always either upgraded me for "free" (except that the upgraded car often uses more gas, so it's not really "free", but I've had good luck talking them into giving me a Hybrid when that happens if they have one available), or gave me a discount for a downgraded car.
I once got stuck in a huge mismanaged queue at Avis for an hour and when I finally got to the front they told me a car was not available. When I said I had booked one so how could this be, the customer service person informed me that I was half an hour late so if I wanted to ensure I got a car I should turn up on time.
Rental agencies overbook just like the airlines, but it's harder for them to ensure supply when people don't return cars on time, at least an airline knows that they can seat 300 people on a 300 person aircraft, the rental agency isn't sure if they'l have 0 or 50 cars on the lot by the time you get there because some people may be late, or they may have sent a lot of cars on one-way trips. It's a tough logistical problem.
I also have no idea why my collecting a car I have booked requires so much typing on their behalf. It is like they are writing a short dissertation on me, every time I rent a car. Surely if I rent another car the same month the amount of typing can be reduced. I have caught a glimpse of their green character based IT terminals and I am pretty certain there is no secret skunk works at Hertz HQ working on anything other than more confusing ways to charge collision damage waivers.
If you rent a car regularly, sign up for the rental agency's premier club. When I used to travel a lot, my company rented from Avis and Hertz almost exclusively, I was in both of their permier rental programs, and when I got to the car lot I could just find the car with my name on it, and drive away, showing my ID to the guy at the gate. The other advantage is that my premier reserved car is *always* there, even if they have to turn away other customers to make sure the car is there.