2002 BMW 330ci buying a used 330 w/ 56,000 miles

I would be asking for a full scan, engine, body control, trans, abs, srs. There are many sections that they can check and report on any active codes or codes in the history file.

It sounds like you're talking about an in-depth certification of a used car. Requirements vary by state but in general all used cars get a safety inspection and any repairs that are needed. Manufacturer-sponsored certification programs don't cover more than that but what they do come with is a warranty to take care of unexpected things that pop up after you buy the car. Many used car dealers offer similar warranties, but regardless where that warranty is coming from, the cost is built into the cost of the car.

Transmissions are just tested on a test-drive for proper operation. Pressure tests can be done when diagnosing a problem, but they are meaningless when there is no problem. Chrysler developed the first computer-controlled transmission and most manufacturers have copied the idea and have similar diagnostics. Part of that is reading on a scanner the volume of fluid it takes to apply each clutch pack. Those numbers provide a pretty good indication of the life left in the transmission before it will need to be rebuilt. That life is in a percentage, not mileage, because driving habits can vary so widely. This is especially useful because due to the design, the computer continually updates the shift schedules to overcome the wear that takes place normally to provide nice crisp, solid shifts. Years ago you had plenty of warning a transmission was wearing out by the gradual loss in shift quality so when the need arose to rebuild it, that didn't come as such a surprise. With these computer-controlled transmissions, you don't get that year or two of warning. They shift solidly until they can't update any further, then you get surprised when a problem develops. Knowing the wear by the numbers on the scanner is the only way to know if the transmission can be expected to be trouble-free for the foreseeable future. Those numbers are likely to not be shared with you because they don't mean anything to the average car owner. What those numbers are good for is providing the insurance company with the confidence to warranty the car.