I've bought Parkers from some of the 'big name' dealers and they looked at me with a blank stare when I asked if they had or could measure the wall thickness.
On a 12 ga #2 frame...I'd be far less concerned with wall thickness. Even if someone had honed the barrels, it would take lots of honing to get into the 'danger zone'. I generally don't buy guns that are that rough, anyway. If the bores need 10 or 20 thousandths removed, is the rest of the gun really going to look that good?
But on a #0 frame 20 I'd be more concerned.