Well...they look real.

They play and save real to so that’s good

I searched wut Pokemon Diamond game cards look like and it looks the same

(and the Pokemon Emerald game card)

Thanks. I just heard I was very rare to own a real copy of emerald years after release

How much did they cost?

It really depends on where you got it. If you got it used at a gaming store or when it originally came out it’s almost 100% the real one. If you got it off eBay or something like that it could be fake. I actually had a fake leafgreen that someone gave to me a while back. You can tell usually with the color of the cartridge. I ended up getting a real one and the comparison is drastic. The fake is like a translucent green and the real one is straight up green and looks super nice. So honestly look up what they look like and compare the cartridges. They look pretty real to me but I don’t have diamond or emerald I have platinum and sapphire💀. Hopefully this helps!! XD