I have an EBJD who is certainly not the patty cake they say the blue ones are. Anyway I went to the store today to see if I can put a regular JD with him. (I know you can but where talking individual fish here). While there I was watching the JD's and the guy asks if he can help me. I told him I was just looking, after watching them for a half hour I picked the one I wanted. Not easy to tell but my best guess he is male. I told him my issue and wanted to know if it didn't work out could I return the JD. He tells me yes and that the weaker JD will change sex and they will have babies 
I have heard of some species of fish doing this but not JD's? Anyone know if this is true or is this guy clueless.

I have heard of some species of fish doing this but not JD's? Anyone know if this is true or is this guy clueless.
the guy is