So basically, I'd tell a customer that the risk is all on them, and that there is a possibility (Probability if using adhesive promotors) that their paint could get jacked up if matte paint.
I'll take that as an official 'I don't apply film to matte paint jobs' on into the future, as you can still get bad feedback from a customer or even sued, even with a disclaimer signed, and I don't need that additional hassle or the money from the rare 1 or 2 times a year it might come up.
