Most important aspects you guys must know are :
a)The product you pay for it, is original or not?
b)The product you pay for it, is good quality and genuine from USA or not?
c)The specification of the film you pay for it is true or not?
1. Ask about USA manufacturer detail.
Maybe most of the tint shops might claim that their products are from USA, but when asking about the USA manufacturer info, no answer will be given. Do some home work, online check on this matter. The genuine brand will normally reveal the supplier of USA manufacturer information.
2. Make sure the product is not "Home-brand" or not original brand.
Some tricky dealer may input other product which is not original one, sell as original product and given a "new name" this call "Home brand". You guys please online check on the original product name and spec before enter the shop.
3. Original Packaging and logo stamp on film.
All original USA product is come with standard packaging and the film is printed the brand logo. Be aware when you can not find any logo on the film when you tint your car.