I think Mike gets a modest finder's fee from the dealer from which he sources your car, though his real money comes from extended warranties, gap insurance, and that sort of thing. Basically, he offers good enough deals on those products that he sells enough of them without having to pressure anyone.
As for the size of his network, it must at least cover the whole Midwest, since I know my mom's '02 Mazda MPV came from Michigan. Still, I think that's just a matter of which dealers he knows the best; I think he can look as broadly as he needs to to find your car, subject to whether the shipping costs can fit into your bottom line.
Once you tell him what you're looking for, he looks for the two or three best ones that meet your criteria and lets you pick one. I don't know how test-drives would work -- I'm confident that if a test drive showed that something was wrong, he'd be the first one to put it back on the truck and send it back, but I don't know whether you could send one back if everything worked fine but you just didn't care for it.
I'll PM you my info tomorrow (the old version of Netscape on my old laptop doesn't like Vortex PMs), but feel free just to give Auto Purchasing a call and ask for Mike Gerard, and tell him I referred you. He's a good, friendly, personable guy, and he'll be happy to talk with you.