Counterfeit

Counterfeit cards are fake trading cards. These can be easily recognized as most fake cards will have oddly colored backs or images or, in a holographic counterfeit the card will not shine when held up to light. They may also have inaccurate ATK and DEF values. Some cards may have a slightly faded look. 1st edition fakes can be identified through the lack of a gold sticker at the bottom of the card (sometimes it is there, but it is silver). However, some legitimate cards are misprinted to have the wrong color sticker. Some cards are easily identified as counterfeit because they are Spell, or Trap cards that have ATK and DEF values as illustrated below. In addition, some may have their rarity written at the end of the card's description or effect, they may be very poorly written, have the wrong font or logo or the image may not be central. But the most common way of identifying a fake is by looking at the stars in the image. If they are irregular and large in comparison to others, it is a fake card.

Fake booster packs/boxes
Fake boosters invariably contain fake cards. Most fake boosters and booster boxes have the following tell-tale signs:
 * Bad picture quality (Duel Terminal cards are often blurred because of their parallel coating and are much darker than common rarity card, as such, their artworks should not be confused with this)
 * Reversed Konami logo
 * Incorrect Format
 * Misspellings (sometimes real cards have misspellings)
 * Wrong card name, effect, Level, artwork, or stats (the name usually is the translated Japanese name)
 * Misuse of English grammar
 * Bright Colouring
 * White bordered text
 * Words that do not occur on Yu-Gi-Oh cards (e.g. one of the cards in the example pictures below uses Adversary instead of opponent and life score instead of Life Points)
 * On boosters, the seals at the top and bottom should be vertical not horizontal.
 * No "English Edition" sign on top of the booster.
 * No gold/silver sticker or sticker is not reflective.
 * False Type/Attribute
 * Incorrect ordering of card type. It's supposed to state the Type first, then the subtype. For example, "Machine/Effect", "Warrior/Synchro/Effect", or "Dragon/Spirit"
 * Incorrect rarity (e.g. Stardust Dragon with an appearance similar to that of a Common rarity), usually accompanied with no kinds of hologram whatsoever since they are depicted as "Common" rarity.
 * Rarity that is not holographic(e.g. a card has gold letters that are not reflective)
 * Strange logo, as in "New yu-gi-oh!" or both "Yu-Gi-Oh GX" AND "Yu-Gi-Oh 5Ds" logo in one pack/box/tin.
 * Numerical code missing in the lower left corner.
 * Sound or gold as an attribute.
 * Copyright 1996 Kazuki Takahashi missing from lower right corner next to the sticker.
 * On boxes, there is a completely unrelated cover card to match the set name, or that the set name does not exist at all
 * On a character's deckbox, a cover card is featured that's not even related to the character in question (e.g. Eye of the Typhoon as cover card for a supposedly Jaden-based Deck)
 * Decks in tins (note that there ARE real Yu-Gi-Oh tins, but they are much bigger then the fake "deck tins", and always shows the cover card that match the tin).
 * Counterfeit cards sometimes feel waxy or have a thin plastic over the picture.
 * Lack of Yu-Gi-Oh! Trading Card Game sign at back of card.
 * Machine-type almost always written as "Maching", and Fiend-type almost always written as Insect-type (do note however that Insect-types do exist, it's just the fake cards sometimes labels Fiend-types as Insect-types)
 * Incorrect writing of Type as well as Attribute (Attributes not written in capitals such as "fire" instead of "FIRE", or a type written with no capital such as "beast-type" instead of "Beast-type").
 * Spell Cards or Trap Cards have ATK/DEF.
 * Cards that claim Exodia as a single card (except Exodia Necross or Exodius the Ultimate Forbidden Lord).
 * Odd, unofficial fonts.