lets go with common names from the start, so we dont all get "yelled at"
it is most likely a sterlet. those have been in common in stores most recently. or it could be a white, or a diamond. a "white" is actually almost 100% black at a small size. sterlets have lighter colors in various areas, and so do diamonds, but diamonds are rarer (no pun intended) so it probably isn't.
those are about the only 3 kinds found in the pet stores, at least as far as the US in concerned. i've heard a lot about the shovelnose on here, but i haven't actually seen one, so i am not believing it yet ...
the link in the post before me is a very good place for info. very accurate. just be careful with using common names / scientific names around some members on here. they have nothing better to do than b!tch and moan.
as for whether or not you should buy it, almost everyone on here will say no. but it's in your LFS, so someone is going to buy it ...
here's what you should know first.
they are hard to keep alive. it will probably die.
if it doesnt die, it IS going to get large. probably over 3' if you keep it alive and give it room to grow. so you will need a tank / pond that can hold it.
also, they need cold water. depending on what kind of sturgeon it is, depends on how cold. sterlets should be kept in water below 75, ideally at 70 or under. whites and all others should be kept in water only under 70, ideally well under that.
and they also need very well oxygenated water. the best way to do that is to have a big tank with lots of surface area on top, and then agitate that water. so basically using HOB filters as a waterfall, powerheads, or bubblers, or a combo of them.
also, they are constant swimmers. so don't keep them with fish that dont do well with constant swimmers. also, when they are small they tend to get stuck wherever they can. between filter pipes, behind / under decorations, basically anything that is a tight fit, they will eventually swim into, get trapped, then die. so give them open space to swim in, and but filterpads between pipes and glass, so they cant get jammed in there.
hope this helps. there are a fwe other threads by people who actually dont hate sturgeon that you can look up, but i think i covered most of it
just curious, what was the size and price?