Posted By:
davidcyclebackMy opinion is the cards should be treated as historical artifacts, and there has to be good non-monetary reason for it to be altered.
If it is known or thought disclosure of alteration, good or bad, will effect market value, it should be disclosed. As far as alteration goes, it's not for the seller to decide what bidders should and should not know. It's for the bidders to be informed and to decide how the alteration effects their bids. If you don't want to disclose what you did to a card because you believe it will effect the sell price, what you did to the card is exactly what you have to disclose.
If for the same price you'd pick a PSA10 over a PSA10 with ink removed from the front, you've answered your question about how 'removal of foreign substances' effects your financial valuation of baseball cards. You value the 'au natural' PSA10 more. It would then be dubious to argue that, while such an alteration effects your valuation as a buyer, it shouldn't effect the valuations by bidders in your auctions and so you don't have to disclose it.