I wouldn't hesitate to take them back!! I got some fat quarters a few years back that were cut so crooked....I didn't have enough after cutting them; and the gal where I bought them gladly gave me some more to go with what I had and apologized for the error. She had let some of her girlfriends help cut them, and I guess they didn't think it mattered that much on the straight edges lol. Not so sure JoAnn's will be as nice; but it definitely is worth trying.
I have never found problems with charm packs from brand name manufacturers such as Moda.