Well let's see MACFISH on wildcichlids.net they were breeding EBJD's and most of the fry came out male.
However females can be found in the industry. For two 90% of males will have a red stripe on top of their dorsal fin with alongated dorsal and anal fins.
Males get bigger and females get fatter in all strains of JD's.
To be honest I think anyone should do their research before buying any fish no matter what they're buying. For one this helps with proper water conditions, heating, temp, nutrition, sexing, and more.
But unfortunately a lot of people just buy a fish cause they think its pretty then it happens to die on them, instead they should of gotten the fishes scientific name and researched the fish for proper care.