The fact that you didn’t get paperwork for it was done for cash isn’t necessarily suspicious . I’m a reputable Llumar dealer and I won’t give paperwork for a windshield tint as it’s legalities are questionable. I have only ever used AIR80 in a windshield because despite its questionable legalities, I’m all for helping customers with their skin issues with a tint that in no way is dangerous for visibility. With that being said, there should be no reason why the shop can not show you the tint with lot number in a “bonified” box for your piece of mind . If they cannot , I would go right to head office and confirm that they at least buy that particular product. If they do, the odds are you are ok. Also as a last resort , if you go to another Llumar tint shop who knows the film lines well, they can look at the job and should be able to tell you just by looking at it with a trained “Llumar eye” .