1892 IHC Rainbow... Altered Or No?

I remain unconvinced that this coin was artificially toned, but it could have been. I recall seeing coins with similar toning back in the seventies and eighties. They had usually spent years, housed in the early envelopes and albums, laden with sulfur content, dating back to the 1930's. Was that toning artificial or dare I say, natural? Does the term "artificial" now speak to intent? Hmmm ....

IF this coin was intentionally toned, it may have been done to mask spots or some other surface issue. I do believe I see a spot or two.

I've not as yet bought a coin from this seller. It's evident from the comments that he's not held in high regard. I tend to judge a coin not by the slab or the seller but by its own merits. With a piece like this one, perhaps a proof as claimed, I'd need to see it in hand, turn it at angles, let the light dance off its surface, etc.