True, but A) I can return the item and B) if I have enough dealings with whatever random company I'm not happy with, they don't get my money anymore.
You're right, many companies make outstanding quality parts that may or may not include instructions. Might be worth it, might not be. But if I'm buying some obscure aftermarket gizmo and the company just "expects" me to know how they intended it to be installed, shame on them.