Hiya,,,yes, I have been to St. Marteen about a dozen times. Here is one shop I frequent:
http://www.Rules.com
and yes, they are very reputable and you won't have to worry about fake cubans. I can't say that about any other places in town. If you have any favorite wines and spirits you can score them at almost 50% off in most of the liquor stores so get the big bottles.