(This reply is more about preventing theft rather than snooping by the dealer, but I figure some members might benefit from this info)
One thing I liked about my '79 Ford was that it had a hood lock in the cab that used the ignition key. When I bought my first Dodge, I saw at the dealership (Glenn Thomas Dodge in Long Beach, Calif. ) that their display models all had a hood lock right next to the parking brake release lever. It was the kind of lock that requires a round key, like on vending machines. I found out that it was called the "Z-Loc", and it's all hardened steel up to the firewall, so it would take a lot of time to cut through it. They install those on all their display vehicles, and none have ever been stolen off their lot. They take it off the vehicle when it's sold or if the customer wants to buy it, they will leave it on. It's part of an alarm system (made by "United States Auto Security") that they install as a dealer option. When I ordered my truck from them, I paid to have them install it along with the full-on alarm system. When I bought my '97 from Dave Smith in Idaho, I also took that truck to G. T. Dodge and had them install the same system in that truck, which I still have.
I don't know if other dealers sell the same thing or if you can buy them from car alarm/stereo shops. Maybe an internet search might find some more info.
Andy