Make sure they do a compression test or better yet a leak-down test. It will give you a bench mark of the wear on the engine. The compression should be 160-170 psi.
An oil analysis is not a bad idea. This will show up any problems with antifreeze leaking into the engine via bad gaskets or porosity.
The third item is a test for leaking antifreeze external to the engine, this is done via an antifreeze additive and a black light.
Doing all three will give you a good idea of how the engine was treated, unfortunately most dealers will probably not bother with any of the three.
Another simple test is to just let the car idle and see where the temp gauge ends up at. With a good cooling system the the gauge should end up between 12 and 1. The dealer can also use his scanner and tell you exactly where the temp normalizes.
The trim gaskets on the rear of the side glass is a common problem. Seems minor, however, the replacement can cost you $2,000 to fix . Corrosion of the gas cap can also be an expensive problem. I would also have them balance the wheels to make sure they are concentric. These are a few of important items to verify. I'm sure that you will get more direction
