I recently picked up some pelligrinis that were obviously steinies because pelligrinis don't have red humps. I have heard pelligrinis are incredibly difficult to care for and require some current and very well oxygenated water. They are said to be much more aggressive and difficult to breed. Apparently so difficult to keep alive and breed that they are almost unheard of in the hobby. This is all hear say so take it with a grain of salt but I would make an attempt to educate yourself about the appearance of the true pelligrini the best you can. You should probably go buy those fish right now though just in case. here is a decent informative link.
http://www.fishchannel.com/media/freshwater-aquariums/species-info/demonfish/more-demonfish.aspx.pdf
http://www.fishchannel.com/media/freshwater-aquariums/species-info/demonfish/more-demonfish.aspx.pdf