Instructions
Look at the label of the card. Since this rookie card is a 1951 of Mickey Mantle, it was produced by Bowman. Therefore, the card should read "1951 Bowman." If the date or the company is different (but does not read "1952" Topps"), then the card is clearly a fake.
Look at the card and examine the coloring. A 1951 Mickey Mantle rookie card clearly has strong colors (see Resources for a picture) and is not faded out. Make sure his name looks correct as well. On an authentic Mickey Mantle rookie card, his name contains bold, white letters inside of a bold, black box. If the card looks faded out anywhere on the card, assume it is a fake card.
Look at the lettering and the picture of the card. Make sure none of it is fuzzy or out of focus. Fuzzy lettering and a fuzzy image means this card is clearly fake and you should avoid it at all costs.
Look at the packaging it is sitting in. Mickey Mantle rookie cards that are legitimate are in a package that states the card is certified (i.e., legitimate). If a card is in anything less, then you want to stay away from this card. The reason is because if a seller is really serious about selling this card, he wants buyers to know that it is actually legitimate and there is nothing to fear. If it is fake, then there is no way for him to prove it is real and he is waiting for someone to fall for his trick.