I forget the name of the dealer my parents went to when we all went on a family vacation. Its in the smaller more expensive shopping mall located off the main road on the other side (away from cancun center) My mum bought a Tag with diamond bezel and they treated my parents to an awesome dinner out in a great restaurant in town as a good gesture.
Regarding customs...... If you do buy, just wear the watch home and mail the empty box back. Thats what I do when ever I travel and buy something. No one can prove that you don't travel with more than one watch at a time and customs cant charge you tax for an empty box.
have a great vacation!! Wish I was going back there this year.
but check out isla mujeres, small island off of cancun if you dont already know it. also, i think this time of year the whale sharks start showing up, you can take a tour and swim with them...
Olé.