To beat the horse again, that it was graded does not excuse the absence of disclosure, particularly where Brent knew the grade was the result of alteration/restoration and that the card had been in a three grades lower holder previously. And I don't think we have the full story on post-sale events.
Oh, and let me add...
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My avatar is a sketch by my son who is an art school graduate. Some of his sketches and paintings are at
https://www.jamesspaethartwork.com/
He is available to do custom drawings in graphite, charcoal and other media. He also sells some of his works as note cards/greeting cards on Etsy under JamesSpaethArt.