Unfortunately you can't take some LFS on their word as they'll put names on fish to make them sound cool or mislead the uninformed - rampant in the marine hobby. Juvies of some species are harder to distinguish so it's best to have something in writing or they may say afterwards that they never said it was that.
I usually ask something that they should know very well; if they don't give an appropriate answer then I put them into the 'doesn't know WTF they're talking about' category.