i used fishing line to take mine off. (30 lb test) left it parked in the sun on a hot day the line cut em off like butter, then you need to clean off the left over adhesive from the car. warming it up with a heat gun also helps, dont go full retard tho, you can burn the paint and bubble it.

whos painting the car? are they not doing the prep work on it? or are you doing the prep and they just spraying it?