This won't take long...
It's called the "Super Pulguero," the Super Flea Market, along Road 2, between Mayagüez and Rincón. A large, peaked-roof, wood and zinc hangar with most of the floor still dirt. Stalls outside offering food and trinkets, and some 60 stalls inside offering from jewelry and pottery to tattoos, computer accessories and even contact lenses.
Open 7 days a week, and on Sunday, the day I visited, the Super Pulguero was open from 8 a.m. to 6 p.m. Why mention this? Because We have this idiocy called the "Closing Law" that limits businesses to 11 a.m. to 5 p.m. on Sundays, with a series of exceptions like drug stores, restaurants, bakeries and mom-and-pop stores, but even in these stores some items cannot be sold outside of the legal hours. (I'd go into detail, but it's stupid in too many ways.)
What's the upshot here? I predicted the sales tax would force a perfecting of the underground economy and noted that flea markets were the visible examples of that process. Now add this: Normal and even expanded business hours; now high-end products and professional services are being offered at cut-rate prices; "mall" format to make the shopping experience easier (the parking lot has lights for night-time customers); the ready chance to open a business in hours rather than months; paying lip service to the sales tax (every stall has a sign on how they "collect" the tax), but cash is the order of the day and the kicker: Municipal policemen as guards in the Super Pulguero.
When the Establishment becomes your partner--whether legimately or not--you have taken a big step from being merely "underground." Push that growing advantage and you will definitely "perfect" an underground economy.
Rest assured, there's more to come.
The Jenius Has Spoken.