I agree that it's important. And you have to know your way around several different models, if not makes of tractors.
I know the prep guy at my dealership, and he's pretty good. More importantly, he takes pride in his work. While I do my own checks a few hours after running the tractor, I really don't worry that this guy missed anything much.
I had bought a 100hp tractor and 15' cutter together some years back. (Another dealer and brand)
The two bolts or pins that hold the drawbar in the center position were missing, or swiped... That caused sway in the batwing cutter, but it wasn't noticeable from the cab. It wasn't long before the CV joint in the main driveshaft that hooked to the PTO started clattering. I mentioned it to the service mgr when I had it in for an unrelated issue. He went to the back of the tractor with me, and after a few minutes said the CV joint was shot, and started looking for the cause, and discovered the missing bolts.
I asked him what they were going to do about it, and he said they would order a new driveshaft assy. They did. It cost the dealer $1500, as they don't sell just the CV joint side of the shaft. You had to buy the whole thing from the PTO to the middle gear box splitter.