I really haven't had a lot of luck with fresh veggies, which I understand are all imported from the same source. Apparently, from what I've read here, the veggies at the roadside stands are from the same source as those at Le Grand Marche. However, there is a Rastafarian farm on the road to Marigot that grows and sells their vegetables. We haven't shopped there yet, but hope to this next trip.
I've found decent veggies at the Fresh Market in Madame Estates, as well as both Grand Marche stores. It just depends on timing. What I have found is that nothing lasts as long there as it does here at home, so I generally don't buy more than I can use in a couple of days.