Topic: Can I or can I not play this game on the 3DS?

A few months ago I bought Megaman Starforce 3 for the DS, and the seller said explicitly that it could not run on the 3DS, just in case I had "mistaken the two consoles" as has seemingly happened before or something.

My curiousity being hopeless, I put the Megaman Starforce 3 cardridge into the 3DS and the game started without any issues, at least for now. Will there be issues down the road, or can I play Megaman Starforce 3 on the 3DS?

@Devanor Yes it can, 3ds can play ds cartridge just fine. I would know since I played my Explorers of Time fully there

@Devanor
"the seller said explicitly that it could not run on the 3DS,"

Hahahaha...
That seller was know NOTHING about 3DS machines.
Yup. 3DS Can play BOTH 3DS & NDS games. But 3DS can ONLY Read Same Region Cart, while for NDS = Region FREE.
And don't worry. It will Not Damage your 3DS.
And... expand your knowledge about gaming. Don't be too Naive or someone can foolish you.

It should run just fine.

Unless it's one of the few region coded DS games (which it evidently isn't), or some weird bootleg version.

The seller was probably just covering their bases. Just in case.

Thanks for all the answers. I was wondering since my DS is quite old, so if it stopped working I could still play the game on my 3DS instead. (as I can with my other DS games, I was just worried that I couldn't (or worse, might end up damaging the 3DS if I attempted it) since the seller said it wasn't possible for this particular game)

As others have stated already, the vast majority of DS games run just fine on the 3DS. It sounds to me like the seller was covering all their bases and/or didn't know enough about the two systems. It's possible that they got it confused with the fact that 3DS games can't be played on the older hardware.

The vast majority of DS games are region-free and should be able to run on any 3DS. The only exceptions are one of the few region-coded games (mentioned above) and games such as Guitar Hero: On Tour that required you to use the second GBA slot (not available since the DS Lite) for an external peripheral to play the game.