If you know how to properly ID them you can refrain from purchasing it until the LFS gets it right. Vocal minority is the main reasoning behind LFS's lack of education.
The most common species to get falsely labeled as O. scyllarus is G. ternatensis, which is actually destructive to reefs when collected due to them living in live branching corals, and the coral being smashed inorder to get them. Please do not purchase, we refrain from talking about them unless it's for identifaction purposes or awaring others of their origin.
You can find details on identifying G. ternatensis
here. It doesn't take a rocket scientist to tell the difference as long as you know what you're looking for. Most notably the red segmental bands and orange meral spots on the dactyls.
You can try either species, O. scyllarus or L. maculata (zebra), however.. you're flat out going to need an upgrade. For one, any biocube is way too small for an O. scyllarus or L. maculata..
O. scyllarus shouldn't be kept in anything smaller than a 40g breeder (dimenstion wise, if you can find a 36x12 surface area, that'll work too).
L. maculata doesn't have a necesarry tank size.. however they need a veritcle sandbed 1.5 times the length of the animal... which at full grown, is a 22.5 inch
tall sandbed.. you can use PVC for that too, however they still need a sandbed to close their burrow up with, not to mention upgrading the PVC as they age can be annoying, especially when it's not a requirement. You're just going to need a really really tall tank to say the least.. I've been eyeing on a 15 gallon tall column tank I've been waiting to go on sale for then I decided to have a go with one, should be large enough.
In regards to how many LFS get it wrong, it varies. If yours is dumb enough to confuse G. chiragra for O. scyllarus then they'll probably get it wrong 100% of the time... it's a matter of what they recieve from their suppliers.
Usually LFS just slap the word peacock on any mantis shrimp they get in.. even if they're aware it's not the same thing as O. scyllarus.
But of course there is always the option of having a smaller species rather than either two. There is alot of variety in stomatopods for hobbyiest.
As far as research goes, skin through some of the more recent threads of this forum and be sure to read through roy's list, he the world's top stomatopodologist (is that a word?) and wrote all the identifaction information and housing requires in
his list.