I've been on this forum for a while, and I have been impressed by the depth and breadth of knowledge of the participants. In addition, I noticed that the background of the majority of the posters seems to be in the sciences, so I feel this is as good as any place to pose this question. I recently had my Model S windows tinted. I walked in to the shop and told the salesman that I needed tint (I already knew that I wanted ceramic). Before I could express a preference, he took me to their demonstration area and showed me their lines. He showed me cheap brand X 70% which had little heat rejection. Then cheap brand X 30% which had improved heat rejection. Then intermediate brand Y 30% which had better heat rejection. Then most expensive "ceramic" brand Z 30% which had the best heat rejection. At that time I told him I wanted the ceramic. Then I got to thinking, how do I know if I am paying for ceramic, yet getting cheap brand X? The salesman is the "expert," so I asked him. He said, there was no way to know, just that I my car would be a lot cooler. I didn't like that answer, so I did an initial search on the internet for "how can I tell if I have ceramic tint," but with no avail. Then I noticed that when I look out the tinted windows with polarized glasses, I get a rainbow effect. So then I did a search that included polarized lenses, and posters on other forums stated that this was a way to verify that you indeed have ceramic film, however the posters who said that did not seem to be well educated or knowledgeable, nor did they use references. That's why I want to use the well educated brains on this forum to help with this question for me and all future internet searches. How can you verify that the tint installer didn't do the switcheroo?