Winter is already blowing cold for retailers. Just this week, J.C. Penney (OTC:JCPN.Q) reported a 26% decline in same-store sales as Kohl's (NYSE:KSS) warned that steep discounting could take a big bite out of Q4 results. Yet neither fared so poorly as Groupon (NASDAQ:GRPN), which fell 29% after reporting a meager 3% gain in European sales during the third quarter. Troubling? Sure, but declining cash flow is far more worrisome. Find out why in the following video.

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