No, there may be some that are not made by nintendo, but they do not have nintendo's seal of approval and therefore may not be of nintendo's quality.

There are many varieties of T-shirts available featuring Mario Nintendo's most popular character be sure to look for the official Nintendo seal on the tag to provide a measure of quality.

All the Nintendo certified games,merchandise,and consoles have the Nintendo seal on it.Even Japanese games have it!

That can only be determined by actually playing the game if the game has modifications like fake pokemon such as Missingno or that the whole entire game has been replaced by some other type of hack then its a fake other than that it should be real.

The official Nintendo DS licensed headphones are designed especially for the Nintendo DS and offer excellent sound quality.