Jen & I live 5 minutes from Market 28, Cancun's main market. It's a great place to shop (Market 21 is slightly cheaper, but much smaller). Tourists flock to this place to buy everything from shot glasses & T-shirts to silver rings & porcelain pottery (photos below).
Almost every day we pass along a road called Tankah, that runs south from Market 28. And almost every day, when we return, we pass a large shop called Plaza 28. And almost every day, when we do, we see a group of white-clad men standing nearby, shouting something about Market 28 at passing tourists.