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Al C.risafulliI'd be willing to bet that every single one of us, at one point or another, has gotten burned by a fake.
Dustin, on the '38 Goudey DiMaggio, here's how you can tell it's fake.  If you look at the card, there's a yellow line that creates a border around the card.  The card stock inside the border is yellowish-tan on the top, and outside the border it's white.
On an authentic '38 Goudey, the card stock is the same creamy off-white color on the inside and outside of the border.  That goes for ALL the cards in the set.  Many of the reprints have white outer borders, and off-white inside.  If you see that, it's a dead giveaway.
-Al