To be truthful, every one of those coins were ordered as to create an air test sampling for my detector and when I was through, I cleaned them. I am not sure where the previous owners got them from but I can assert that I completed this cleaning on my two prior dug silvers that I had thought were as clean as I could get them and they turned out even freaking shinier!
I will say however that you are right in regards to some toasted coppers as I tried this on a Matron Head Large Cent and although it shined up really well, the detail left right out the door. I made a replacement patina using yellow food coloring dye and sanded rust, dabbed one side of the coin and allowed it to dry completely, then I steel wooled it to bring back the detail and sprayed a layer of clear coat to seal it in. Don't worry, I would never try to pass it off as authentic but it does look pretty good lol