A bounce off the oft-quoted Latin phrase "caveat emptor", this one feels a little more appropriate in the age of Napster-aided consumption. "Caveat kleptor" would translate to "stealer beware," except that the kleptein root is actually Greek. A quick and dirty check on Latinate roots for "thief," "steal" or "rob" reveals candidates like latro and raptor, which would mostly remind English-speaking audiences of restrooms and dinosaurs, respectively. So this one feels like good memetics for now.