I answered a similar question before, here’s what I put:
Here's some warning signs when buying cartridges:
- Does it look new? Any wear? If it's lacking wear, it's probably fake. They don't make new old games.
- Is the sticker slanted? If yes, it was hand-put on. This doesn't always mean it's fake, but it definitely means it's been tampered somehow.
- The price. Older gems, specifically Gen 4 and 5 games are valuable, typically pricey.
- The Quantity. If there's more than 10 for sale by the seller, assume it's fake.
- If the seller claims it's new. Gen 6 and lower games are too old to be new. If you find an unopened box copy, chances are it'll be for sale in the 100's
Here's some tips when buying old games:
- Buy local. This way, you can test the game out to make sure it works.
- Know the value of the game. Knowing the game's value in your area can help you know if you have a deal, or are about to be ripped off.
- Signs of "aged" cartridges are good. Slight scratches and tear on it proves that it's been through a long, working life, make sure it works of course, but imperfections are a good thing when looking for authentic cartridges.
- Seller's history. If you're buying online, make sure the seller has a good reputation, and isn't selling millions of the same game.
In conclusion, if you think it's fake, it probably is.
Also note, if you get the game new and from an official store, chances of it being fake are low. Old GBA games freeze on certain frames if they’re fake, too
Also please excuse if the formatting is poor; I’m on a new phone and I have no idea how to use it.
Hope this helps!