3.0 How will I know one when I see one?
There are a few guidelines to follow when identifying a suspicious looking card. For the most part they are obvious, but for the benefit of the slow, here they are.
Obvious Rule #1:
Most fake/altered cards are in Mint or Near Mint condition. It is more difficult and less profitable to fake a played card, and usually if a fake goes unnoticed and is played, it will not live as long or wear the same way as a normal card, so slightly played ones are easily found out and discarded.
Obvious Rule #2:
The more valuable or useful a card is, the more likely it is to be faked/altered. If you get a pile of cards from someone and you have reason to believe it contains fakes, don't worry about the Gray Ogres. Stick to examining the Power 9, or the hot Type 2 cards that are in the bunch. The only reason you might find a fake of a stupid card is if it was a card they had practiced on or was part of a larger, professional counterfeit operation, in which case chances are good the whole stack is trash.
3.1 My Mox looks a little weird, is it fake?
Not necessarily. As with anything in the world, no two things are exactly
identical. Thousands to millions of the same card are printed which gives
way for slight variation in cut, color, sharpness or anything else that may
vary in the card-making process. It is common for cards to be darker or lighter
from each other and sometimes have a slightly different tint. Other times the
gloss is a little different, but not enough to mark the card. This
was true for the first run of the Mirage cards and for some of the Antiquities.
In addition the corners of the cards may be a little bit more/less rounded than
your other cards. Very few Magic cards have perfectly rounded corners.