Everybody I work with at my LFS know a lot about fish, but not everything. The one guy told me electric catfish grow a foot. The truth is, the microstoma species does, but LFS only really get electricus species in which have grown up to 39". I wouldn't give up trusting them because of that.
You cannot expect minimum wage hobbyists to know the difference between all closely related species. 99% of the time I would not be able to ID an African cichlid if I didn't see the name. Prolly a little more likely to know central American's apart though. I see as much variation in a species as I see in different cichlids.
It's one thing for them to hire some guy/girl who doesn't know about fish, but you cannot expect somebody who has to work 9 hours a day, 6 days a week just to pay their bills, to have much time to research fish on their own.