Just make sure you tell him exactly why you want the windows tinted.
I know that sounds basic, but the shop I used to work for never really asked that of the customer... or at least not enough. We would get to the job with one type of film, talk with the customer for like 5 minutes and find out it wouldn't do what they were looking for.
Granted, that is the job of the person doing the estimate, but while it's not 'rocket science', evidently it could be missed.
Since I'm on my own now, I make dang sure I know what the end result is that the customer is looking for.

RoAcH