It's important to be an informed consumer, but I don't think you can fault those guys for not knowing how long it takes to get a purple belt. Some of them might come from martial arts that advance you quickly. Some of them might see Khristian's jiu jitsu (which must be at the blue belt level by this point?) and how easily he could tool a noob and think that he's legit. If they have nothing to compare it to, it might look like the real deal.
I don't know anyone who is brand new to training who walks in and truly understands the time commitment it takes to get a black belt or the level of a purple belt relative to white belts, this take time in the right environment- which those guys didn't have.
I had no grappling experience or fighting experience when I started. I had no idea how long it took to progress, how good black belts were, or any of the nuances of the sport before I started BJJ. However, I made damn sure I put in my time researching the school, the instructor and the sport before I signed up at a school. Sure I didn't know how good a purple or blue was relative to a new white belt, but at least I knew the colored belts at the school were legit. Anyone that doesn't do the same risks training under a guy like Geraci. Geraci is the most at fault here, but these guys should have done their homework. They should be embarrassed for getting scammed, and Geraci should be forced to pay back their fees.