I have never seen any evidence that Dominican Cohiba's are being faked. That is not to say is doesnt happen, but a retailer has very little to gain by selling fakes. I have only heard of Padron and Opus fakes in recent memory.
The only way to know you are purchasing authentic Cuban Cohiba's is to know and trust your vendor.
Cigars can easily be rebanded with authentic labels and packed in legitimate boxes. But a trusted retailer will not risk reputation and future sales to trick a few unsuspecting souls.