They get huge and needs lotsa swimming room. They grow very fast, so if you get one you will have to eventually
1. euthanize it
2. buy or build a monster tank on the order of 4000 gallons
3. get somebody to take it
I want one too, but it is very dumb for fish stores to even consider selling these. Only zoos and oceanariums can really keep one of these for life. Maybe a casino or restaurant with a monster tank. The only person that can keep sharks that big is Novice and even then that is kinda pushing it for that shark, they swim almost non-stop.
I've been really wanting to buy one myself, buy you just gotta say no. Even if you do find somebody to take it, how do you think you're gonna transport it. They grow pretty quickly. Most places won't want to accept your shark anyway, believe me. This question comes up all the time. Your tank is too small for any shark for life, a bamboo or epaulette or catshark would be alright for a while, but would eventually become too cramped in that tank after only a couple of years.
Buy the book Aquarium Sharks and Rays if you are truly serious about keeping sharks. It is by Scott Michael, you should be able to find it online or possibly your lfs may have it.