The general consensus seems to be, if it's not from an LCDH store, it's a very good chance it's fake. Here's a list of the LCDH stores in the Caribbean
La Casa del Habano (drop down Geographic Zones and choose Caribbean)
I think there was said that there is one resort that had genuine CC's in Nassau, can't remember the name though. It was in another cruise thread asking about Cubans.
Edit: Missed that you were going to be in St Martin, Netherlands Antilles. Here is the address for the LCDH there from the site.
Address: 71 Port La Royale. Marigot. 97150. Saint Martin. F.W.I,
Telephone: 590 87 5894
Fax: 590 87 0299
Email:
casa.del.habano@wanadoo.fr