The "scam" in question consists of buying fashionable clothes (which the article says have a very brief vogue during which a store can hope to sell them) with the intention of wearing them once and then returning them for a refund. Presumably the worst serial offenders wear an endless succession of new clothes at (effectively) no charge.
For a particular instance of "buy-wear-and-return" to qualify as a scam—that is (according to Merriam-Webster's Eleventh Collegiate Dictionary), "a fraudulent or deceptive act or operation"—the guilty party must intend all along to use the clothing without paying for it. Otherwise, the scam becomes indistinguishable from second-guessing or buyer's remorse.
The observation that stores consider the practice "no worse than stealing" is, I think, ludicrously self-evident—just as the observation that stores consider the practice "no worse than firebombing an upscale fashion outlet" or "no worse than murdering a clerk" would be. Of course it isn't worse, since at its most heinous the practice leaves the store with a slightly worn garment that is unsellable owing to the fickleness of fashionistas; in contrast, outright stealing leaves the store with a coat hanger.
My guess is that the reporter meant to say that the practice "is no better than stealing"—but she blew it. Initially I thought that "no worse than stealing" might be some sort of reversed-meaning idiom in the UK, but I was pleased to see that a commenter from Wiltshire responding to the story on the Daily Mail's Website succinctly wrote, "Stores say it's no WORSE than stealing? Surely you mean no BETTER?"—and drew 41 up votes from other readers (versus 3 crabby down votes).
The simple answer to your question is that "no worse than stealing" means exactly what you'd expect it to mean, but that the reporter in this case meant to say "no better than stealing."