Super Rare 1988 Donruss Diamond Kings Edition Mark McGwire #1 With Very Rare Error

This 1988 Donruss Mark McGwire Diamond Kings edition baseball card is definitely a gem. Not only does this card belong to a very sought after edition being a sketch card, it has an extremely rare error on the back of it. I personally have never seen an error so rare. I have also done extensive research on this particular error and did not find anything like it on the net. I've called multiple card shops and blew their minds when describing the error. So that being said going along with the basic knowledge of the value of all things, the less there is of something the more valuable it becomes, I have priced this card as such because I believe it is worth the amount.