I'd thoroughly clean the glass that is to be tinted and check for any scratches in the glass. Many shops go over the glass with a razor blade and scratch the glass while doing it. Had two shops have to replace glass because of it. One was on a new van (still had the plastic over the carpet) and was told the scratches were already there and the tint just made it obvious. A couple weeks ago a second shop said the same thing after I noticed scratches between the film and glass. I reminded the second shop that they were the ones who unpackaged the new glass and was the only ones to touch it since it left the factory. Then they asked "Are you sure it was new glass?"
I had a local officer here that overheard the story and he mentioned that he also ended up noticing scratches in his new truck glass but since he didn't actually check to see whether or not the scratches were there when he dropped it off, he didn't push the issue. Anyway do yourself a favor and check your glass thoroughly prior to any window tint service.