I think you are talking about the processes that I would be doing: grinding, blasting, and rust paint.Unless they specialise in restorations (maybe), they are mostly going to be concerned with just quickly welding in a fresh piece of steel to patch up the hole and extend the life of the vehicle for a few years (or over here, most likely just get it through an MOT for another year).
It might get a coat of weld through primer, which will mostly all burn off the moment its welded in and start rusting.
They are unlikely to spend a lot of time cleaning all the rust off the non visible areas of panels - only what is needed to make a functional repair.
If they are half decent they might shoot some cavity wax in when done, to give it the best chance.
To properly protect repair panels, takes a lot of time and effort, you usually end up trying to clean up very difficult to access areas, often just having to do the best you can.
You have to carefully design and plan the order you are going to weld in replacement panels so you can get to the back of them to coat it with protection (for example, epoxy), you may have to wait periods of time in-between for stuff to dry off.
Spot welded seams can present a number of challenges for stopping rust starting between the layers.
Somebody could spend 5 times as long and 10 times as much as doing a quick patch job, yet visually it will look the same from the outside.
They won't get paid any more for it and most people wouldn't care either way and unlikely to keep the vehicle very long, so why bother?
If you are going to pay somebody to go over every square inch of the car eliminating rust from every nook and cranny, you will need to find a specialist and have very deep pockets.
Chances are you can just deal with most of it for minimal cost yourself with some simple products, without cutting out and replacing all but the worst of it, and achieve much the same net result.
All the person has to do is just weld, no grinding necessary.
I may even just hammerform a new piece of metal using that lower trunk part as a buck (directly on the car), cut out the old 24 yearold metal and just bond/weld new metal in.
Btw based on my experience chemical rust removers are not effective in removing 100% of the rust.
I always paint rust paint within 8 hours of the area being sandblasted.