As long as one is buying Amphilophus from a reputable dealer, chances are they are going to be selling pure fish. With the access to wild stock from both species this is not an issue as much as it is when buying fish from your local Petsmart. (or offspring from those fish)
As far as the photo in the previous post, that image comes from an article that Paul Loiselle wrote over 40 yrs ago, and much of the info from that era no longer applies to what we now know today. Fleshy lips, and pointy snouts does not neccessarily equate to A. labiatus.
Read the following sticky and you will understand why.