While you may not need to worry about buying fake Game Boy Advance games from popular electronic retailers such as Walmart and Best Buy, cartridges purchased from online and third-party sellers occasionally present problems. If you purchase a game from an international seller based out of East Asia, for instance, and it comes without a box or instruction booklet, or you get a game that doesn't work, you will have to determine whether you have a fake GBA game on your hands.
Check the game's title using the list of all official Game Boy Advance titles released in the United States, Japan and Europe at GameFAQS.com. If you do not find the title on the GameFAQS list, it is likely a fake GBA game.
Look at the cartridge to see if it is authentic. Game Boy Advance cartridges should be made of black plastic. Near the top of the cartridge, you should see a curve with the words "Game Boy Advance" written under it. Beneath that, you should find a sticker with the game's title and a picture. For example, the sticker that appears on the cartridge for "Super Mario Advance 2: Super Mario Word" bears an image of clouds and the game's title.
Check to see if the official Nintendo Seal of Quality appears on the game's box and the cartridge sticker. All licensed GBA games have this emblem. The seal should appear on the back of the game's box in the bottom center and in the bottom left corner of the cartridge. See Resources for an example of a fake Game Boy Advance cartridge.