My wife and I have been to Cancun 4 times in the last 8 years and love it. As John said LCDH is the one place to be sure you’re getting authentic product but theirs also the Duty Free shop at the airport and.......wait for it......Walmart has a small walk in Hummi. I have a hard time believing either would willingly sell fakes. Of course we all know not to buy anything in a glass covered box! With that said; I remove the bands and bring my on every time. I do buy some Edmundo Dontes every time I go, always from LCDH.
We learned the ropes on our first trip. Even if you are staying at an all inclusive you should go down town to visit Market 28 (the only market worth visiting, IMHO) and eat at Laperia at least once. If you are staying in a condo; go to Walmart the day after you check in. Prices are ridiculous! We buy enough for breakfast, most lunches and few dinners and of course plenty of beer, booze and crap for happy hour. Our experience has been that most people staying in codo’s do the same.
We’ve done all of the day trips and enjoyed most. You can’t beat the snorkleing at Contour or Isla Mujera (sp on both?) and the ruins are worth seeing at least once and after being in salt water for a few day visiting a cenotes is like heaven. I hope you enjoy your trip and no matter where you go; savor the local flavors!