thats some crap and how do i know if they are bad hacks?
You can only tell when you have a bad hack when your game starts to mess up, the safest way to get pokemon from the GTS is to breed them, release the one you got from the GTS and keep the child.
In theory this is safe because the only things the child inherits are IVs, Nature (if the mother holds an Ever-stone), type of pokemon and moves.