For small text & thin lines I wouldn't use a removable adhesive (RA) vinyl, or an air release wrap vinyl. I'd use permanent adhesive sign vinyl. The adhesive is more aggressive, it's thin, so less chance of everything snagging it, no lam needed. No long points on graphics, round them all off, widen out any that are just too narrow, and post heat to set the adhesive before they take it to the car wash. Also, if the customer is installing, are they just using glass cleaner? That can leave a residue. Glass often needs to be cleaned more aggressively than painted surfaces, especially on vehicles, and even more when doing fine line stuff. Also rear windows on any vehicle I do, if it has a wiper, if I can't pull a fuse/ plug and disable it, I pull the wiper arm right off it so they can't screw everything up with it... You know they will.