I live close to cancun, and i can tell you that if you like Watches or Cigars this is the place. But wet shaving related products are none. BTW i could go if we make an interesting group 5-10 people.
Cancun is a great place to vacation, but outside of overpriced trinkets there's not much worth purchasing.
If you want silver and local crafts, rent a car and drive out to the countryside (or even Tulum if you have the time), there'll be much better deals for you.
In fact, you should rent a car anyways and go see the ruins. Your resort will sell your tour-packages, but you'll spend as much time as the driver's brother's road-side store getting hustled as you will seeing the sites.
You can find Brazilian Made Gillette Thin razor blades. They come in a red package. Those are hard to come by in the states and are very sharp and smooth.