sorry man, it seems thats the way the game is played. It's their (wrong) way of "weeding out" the people who just want to abuse a car on a test drive. I 1/2 don't blame them. the other 1/2 hates them for it but having sold a used car, I can understand that they have to have SOME way to try to filter out the flakers.
What kinda car are you arriving in? When I pulled up to the Honda dealership in my 02 RSX-S that was just fully detailed, they gave me the keys to their only Si coupe on the lot and said "have fun". I was probably 22 years old at the time but I'm sure if I had pulled up in a beater-ass car they would have ridden with me. They've since gotten to know me and will pretty much let me test drive anything I want w/o even having a salesman in the car with me.
I realize that's a

y thing for them to do cause who's to say I don't have money just based on what car I pull up in... but hey, that's the game.
Try another dealership... one will take you seriously eventually. Not sure what kinda clothes you wear or what your demeanor is when you go into these places but if you want to be treated differently, you may consider these things if you haven't already.