In all fairness, I do not know a painter or powdercoater who sands off the face of the wheels after treatment.
Unfortunately, this really is down to the car owner I am afraid, unless you specifically ask them to do it.
This is a regular bone of contention in my shop when we have to spend time removing the paint/powdercoating from the wheel inner face.
We use a finishing sander with 40 grit (as below) or a random orbital sander which is better than an orbital sander for this job and takes about 1 minute per wheel.