Can't say anything on the professionalism of Pakistani workshops. I think there capacities are limited to trial and error approach. As I am myself not of the relevant field can't say what they have done here but comparing it to my field of construction.
I know that most of the contractors constructing small residential and commercial buildings work the same way. They will construct the structure based on their own understanding (or thumb rules) and ignore the engineering details of steel binding, concrete mixing and then start giving you guarantees like if something happens to the structure they will handle it.
Something similar is happening here I believe. The workshop has cracked a way of keeping the car stable and vibration free and they are selling it backing with warranty.