Its great that they all say this, but is there anything in writing saying that the application doesn't damage Paint.
Giving my customer "My word" that it wont damage it is 1 thing, the manufacturer noting it would be better.
You're totally missing the point here. There is too many variables for an absolute guarantee. The manufacturers pretty much limit their liability by stating that the vinyl will not damage factory applied OEM finishes. To my knowledge they do not put this in writing because even factory applied finishes have been known to fail in the past (anybody remember the peelers from the late eighties and early nineties?).
You need to be honest with your customers and
not give them your word that there want be damage there paint. Be honest and say that there is a remote chance but is a very rare. And also tell them that it will not damage OEM original paint that is in good condition. If the car has ever been repainted because of an accident, the chances a little higher than it will damage the paint.
Because of this, need to clearly state these facts on your work order, and also specify that you are not responsible for any damage. But verbally tell them that it is very rare that paint damage occurs on removal.
This second thing concerning removal, is you need to use the proper technique when removing their wrap. The vinyl should be warmed up a little (not cold) and you need to pull the vinyl back against itself and NOT out at a 90° angle.