Although I think that a beta can make a bad story better - or at least point in the direction... I fondly remember a handful of 'rewrite *that* and *that* because it sucks/makes no sense' comments that were really spot-on. Ok, make that a beta can make a mediocre story better. If it's bad to the core, there's probably not much hope (I beta read for a certain site a while back, and there were a handful of stories where 'scrap and write something else' was the only honest response...