OK, it is a pet peeve of mine that these are called sharks. :hilarious
If you want a giant catfish in your tank, then that is great...but they are catfish, and not sharks
I would not consider them reef safe. I would consider them a threat to lots of things because they would not be all that picky (consider how people fish for catfish).
They will likely not eat corals...but they get large, and may bulldoze or cause other problems in a tank. Like other catfish, watch for the spines in the dorsal and pectoral fins.
IMO, for any LFS to sell an animal with this misinformation, it is personally a sign to shop elsewhere. It is one thing to say "hey this is a catfish and can live in saltwater" and another to call them a cat shark (which is a specific type of shark in the hobby).