Car stuff isn't IKEA, most systems are pretty much the same and everyone modifies their car differently. Trying to cover every way in which someone might have modified their car prior to the latest gizmo is simply more work than it's worth.
Documentation costs a TON of money. Lots of smaller shops simply cannot invest in good instructions. Expecting someone to know the basics isn't too much. A first time install will always have a learning curve and trying to eliminate it is a fools errand based on my very extensive experience on the matter.
If the average person wasn't so below average it would be easier to provide instructions
:rofl: