There are a lot of window films on the market today. Some good. Some....not so good. But, how do you determine the difference when everybody says "Mine's the best."?
Start with the warranty. Make sure the warranty is backed by a reputable manufacturer. Films from over seas are often not supported by a comprehensive warranty and can be difficult to deal with should a concern arise.
"It doesn't matter how well it looks, if you don't like the way it looks". While some films will stop more heat than others, they may not be too attractive on your home. Give serious consideration to the appearance when selecting a film.
Most window tinting companies are happy to provide references. Be assured. These are always satisfied customers. Take things a step further. What associations are they a member of and are they bestablished in the community? (BBB or Chamber of Commerece)
But in the end, go with your instincts. If what you are being told sounds too good to be true, it probably is. Be a wise consumer. Get to know who you are doing business with.