We used the free coupons from the ship at all ports in Mexico. You have to go to the specific store. One said free diamond earrings, another free tanzanite earrings and another a free "gift".
We did not have to buy anything, but they will only give one gift per coupon/newletter. My girlfriend forgot her newsetter and showed her room card and that worked. It was a pin that said Mexico.
The free diamond earrings are real, real small. Looks more like small chips or scrapes of diamond. The earring studs holding the earrings was bigger. Same with the tanzanite earrings... very, very small. Oh well, it's free.