Assuming that there are LaRue markings on it.

First thing: Call Mark (512-259-1585) and tell him that you accidentally bought a knock off and that you wanted to make him aware that this guy is selling illegal "LaRue" stuff.

Mark will go off the handle, he may swear at you a bit - but get him to understand that you aren't asking him to fix it, but that you wanted to let him know that this guy is infringing on his copyright. Give him the contact info for the guy that sold the stuff to you.

Mark (or one of his minions) will handle the fun stuff from there.