OK, under the DMV VC Subsection 26708 (a) (1-3) 26708.
(a) (1) A person shall not drive any motor vehicle with any object or material placed, displayed, installed, affixed, or applied upon the windshield or side or rear windows.(2) A person shall not drive any motor vehicle with any object or material placed, displayed, installed, affixed, or applied in or upon the vehiclethat obstructs or reduces the driver’s clear view through the windshield or side windows.
(3) This subdivision applies to a person driving a motor vehicle with the driver’s clear vision through the windshield, or side or rear windows
So, just by definition of the first line, they could be d***s just for having anything on your windows in the first place. Then, lower down in section 10:
(10) Sun screening devices meeting the requirements of Section 26708.2 installed on the side windows on either side of the vehicle... has in his or her possession a letter or other document signed by a licensed physician and surgeon certifying that the person must be shaded from the sun due to a medical condition, or has in his or her possession a letter or other document signed by a licensed optometrist certifying that the person must be shaded from the sun due to a visual condition. The devices authorized by this paragraph shall not be used during darkness
States you have to have a doctor or optometrist's permission to have it, and can not use at night. Technically, under the letter of the law, perforated window film is sun screening, and if they wanted to could tell you to remove it when driving at night.
Perforated window film can also be classified as a film or tint. Which varies by state as to the legal light transmittance allowed, but:
(d) Notwithstanding subdivision (a), clear, colorless, and transparent material may be installed, affixed, or applied to the front side windows, located to the immediate left and right of the front seat if the following conditions are met:
(1) The material has a minimum visible light transmittance of 88 percent.
(5) If the material described in this subdivision tears or bubbles, or is otherwise worn to prohibit clear vision, it shall be removed or replaced.
Regardless of state to state bylaws, I think it's pretty clear that if you the professional installer are not providing a product in which the driver has a clear and unobstructed view, then you (the business) can be held liable. Because if someone backs over a kid in a driveway, and says they couldn't see because of dirty filled holes in their window film... guess where the finger is ultimately going to be pointing at?