Do you happen to know what species the fish at your LFS actualy are? Can you get the scientific name?
The gourami mentioned as being dyed on Death By Dyeing is not actualy the 'honey' gourami but colisa labiosa - the thick-lipped gourami.
I have heard of honey gouramies (colisa chuna/sota) being injected under the dorsal like you've described with a blue dye. However, there's also a natural color morph of the dwarf gourami (colisa lalia) that has a very similar marking on the dorsal. Still, I'm sure they could try to dye dwarf gouramies as well (surely with incredibly high mortality rates that don't make it a profitable thing to do but you never know).
Seeing as they've been called 'blueberry' gouramies ('blueberry' being very commonly used to describe dyed fish) I would assume that the fish in stock at your LFS are indeed the dyed honeys and not the natural dwarf morph. On the other hand, I've seen dwarfs called all sorts of ridiculous names as well.
You say they only had the purple marking? What about the body color? The dwarf morph has a red-orange base color with the blue near the dorsal. A dyed honey would also look yellow/gold/red with the marking but they don't develop the body color until they mature somewhat so maybe this acounts for your discription seeing as you haven't mentioned any characteristic background color.
You should probably just ask the LFS itself what they are and if they are natural or dyed. THEN you can kick up that fuss

I'd tell you to post a pic but I don't know how useful it would be in determining whether the fish is dyed or not.