As cool as sharks are, they have very specific requirements... And the biggest requirement is tank size. They need a minimum of 180 gallon tank and that is just for bamboo sharks and epaulettes. Smoothounds and wobbegongs need at least an 8' tank, and leopard sharks and requiem sharks need their own pools.
I don't recommend buying a shark and saying you are going to upgrade because 90% of the time it doesn't happen. Why not just save the money on a smaller tank and buy a larger one to begin with? And don't expect zoos or aquariums to take any sharks... they won't.
I would say the guy at the LFS was just trying to get rid of a shark and not take a loss on it.