I purchased a Schwinn basic rack trunk/pannier set from Walmart a few months back for $24.99. I've used it to commute back and forth to work about 30 times and have taken it on one overnight trip for which I did not have to pack it very tight.
I'll bet you got 25 more uses out of that bag than the guy with the next most uses. I doubt Walmart return folks will have any idea how to evaluate your claim that it should last more than 30 uses. I'll bet the Schwinn folks aren't going to waste a half hour of labor evaluating your claim either - since that would probably cost them more than giving you a new bag... which I don't think they'll do; although they might ask you to send the ripped one to them first before they tell you it's your fault and give you a $5 coupon or something.
In better news - I've probably got two or three thousand commute days with my Ibera bag and it's holding up well... getting a little saggy maybe.
