I just got my 09 328i tinted here: Winners Window Tint LLC > Home
. That's just to show you an example of what to look for. They have a number of certifications. They also have a lifetime warranty. When you walk into a store, make sure the area is clean and presentable. It's impossible to get good tint adhesion in a dusty dirty shop. They should also have hundreds of pictures of their work. That means hundreds of customers which translates to good word of mouth. The shop I went does computer cut tints. Not sure if that matters. But, my tint looks as if it came from the factory. No bubbles or creases, etc.