Talk about a tourist trap; the shop keeps were money-grubbing and aggressive. Every time you tried to leave, they'd start making offers, taking 10, 20, 30% off on an item you were only casually looking at, saying anything to stop you. Often times if you're in the mood to haggle, you can cut the price of anything they offer in half, whether it's a $10 trinket or a $1,000 chess set, everything is COMPLETELY overpriced, and you're expected to haggle.
Even after haggling over something you really want, threatening to walk away, actually walking away then being offered a better deal, etc - I still came away from the port feeling like I had been ripped off on everything except the tequila (where the prices are set, non-negotiable, and in line with the cruise ship and every other duty-free port).
Unless you're planning to do some diving, sightseeing, or buy some tequila, then Cozumel, and most of Mexico, really don't have anything to offer.