I posted these examples before... I'm not saying this is the case every time it's just ONE example.
That being said; I took these shots one with a $100 B&W filter, and the other with a $3~5 grab bag filter. The grab bag filter had a bunch of scratches, and was even a little warped. The funny thing is, it's been a while since I looked at these and I'm not even sure which one is which lol. Can you tell?
Edit: I remember which one is which now... the little flag was waving in the background it's in one shot but not the other...