These types of tricks will work less as the agencies continue to have less trouble filling cars. As it is if you book a compact you are probably better than 50% to get a car better than a compact. And the difference between the compact and two levels up is fairly insignificant anyways, often it is something like going from a Focus up to a Stratus or maybe an Intrepid. Besides if the computer shows you are anything close to a regular customer, they probably would give it to you anyways if they have the cars available.
As for the 25 thing, I remember those days and having to pay the fee. Generally best you can do is just shop around and try to find some small independent outfit in any given city. They can sometimes waive the fee, but all the majors have no choice because it is part of the stipulations of their massive liability insurance policy that they must keep. There is no law that says this must be done, but they would lose their insurance policy if they didn't follow it.