One way to make sure, if you are traveling abroad, especially in Central America, the Caribben or S. America, always visit a La Casa de Habana store. They are the official-run Cuban stores that you can trust, they sell only the real thing, but you will pay full prices for them.

As for online purchaeses, we're not allowed to discuss how to illegally import Cubans into the US on this board, so I can't answer that.