I've noticed in certain Walmarts my signal won't work no matter where I am - more than likely the thick walls I would assume were blocking the signal not some malicious attempt to stop me from price matching.
If stores got truly desperate, they could block cellular signal in stores and provide open, free Wi-Fi. I already can't get signal in most grocery stores, since they're huge and seem to have Faraday cages built into the walls.
