Joffas16 said:
You could try Amazon, I know there are at least
fewer bootleg GBA games there (because sellers have to maintain a good customer rating or they get booted from the site). You pretty much just have to be cautious. If the description says the game comes with a manual, it's most likely not a bootleg. If the price seems to good to be true, it most likely is a bootleg. It's always a gamble unfortunately. The good thing about Amazon is, you're more likely to get a return if you run into one of those cases.
Once upon I time, I even saw bootleg cartridges at Game Stop (it was Fire Emblem), some sellers just don't even know they're selling fakes. When you get the cartridge and start it up, and the game has gotten some love with three used files, two of those are epilogues, you know you most likely have a genuine copy. Those getting called "used" but have all blank data raises a red flag.