Took 8 to a local polishing shop, 3 should have been a slam dunk and needed 1 of the remaining 5 to be salvageable. Received back 3 very mediocre, 2 destroyed, and 3 untouched, and charged $350. He cut windows out of the back in an effort to get behind to knock out dings (destroyed those).
Found out about Rick Miller, sent all rings to him, he asked if I wanted to do all 8, explained 3 would be driver quality but the remaining could be restored. Rick didn’t let out too many secrets but did explain to me he is partnered with someone and removes the back ring during the restoration.

All polishing shops are not created equal
As noted, getting the backs off is key to doing a good job, and a trick to do correctly.

Only know of one other fella that does these and as I remember he did it for his own projects and was pretty backlogged with friends rings. Been years since I’ve heard if he does this anymore.