Can I ask if you bought the cart on Ebay, or if you bought it when it came out and used to have the original case/manual? I ask because there's a lot of fake GBA carts out there and it's hard to tell them apart sometimes. As long as it isn't an Ebay copy that was sold by a seller in China.
I will answer for all the GBA games I have up, Final Fantasy Tactics I bought brand new but I lost the case and such awhile ago. I bought the other three used on Amazon a few years ago for my DS. As far as I know they are not fakes, but I do not have the original boxes. Last I played them the games worked fine and they have been in my DS case since then. I just don't play my DS these days.I didn't even know you could get fake GBA games from China.