I'm still very skeptical as to how many of the proclaimed "bad HuCards" are actually bad.
Usually sticking a piece of tape, cardboard, credit card, whatever, underneath the pin area when you insert the game will cause proper contact to be made and cure a lot of this sort of stuff.
Cleaning, sanding, etc, seems to take care of the rest of it.
In certain hardball cases where you just can't get the game to work, taking it and trying it on another console reveals the game actually works flawlessly.
I'm of the belief that as these consoles get older and the cart slots see more and more use, the internal pins get bent out of position, they corrode, get dirty, etc and cause issues with certain games.