When you do find a shop, ask them if they follow
this,
Specifically the parts of RCW 46.37.430 that say:
The maximum level of net film sunscreening to be applied to any window, except the windshield, shall have a total reflectance of thirty-five percent or less, and a light transmission of twenty-four percent or more, where the vehicle is equipped with outside rearview mirrors on both the right and left. Installation of more than a single sheet of film sunscreening material to any window is prohibited.
and
A person or business tinting windows for profit who tints windows within restricted areas of the glazing system shall supply a sticker to be affixed to the driver's door post, in the area adjacent to the manufacturer's identification tag. Installation of this sticker certifies that the glazing application meets this chapter's standards for light transmission, reflectance, and placement requirements. Stickers must be no smaller than three-quarters of an inch by one and one-half inches, and no larger than two inches by two and one-half inches. The stickers must be of sufficient quality to endure exposure to harsh climate conditions. The business name and state tax identification number of the installer must be clearly visible on the sticker.
A lot of shops screw their customers over by doing an illegal tint job.