Let me offer my opinion, and feel free to ignore it if you want.
First, Leopards are generally colder water sharks (55-70 degrees). They are found in wamer water, and can even tolerate reef temperatures, but for short periods of time.
Second, Leopards grow to 6-8 feet in length. If the ones you saw were 8", they were truly babies. At that age they are not very aggressive and may have trouble feeding if thrown in with more mature, aggreesive fish.
Third, Leopards grow fast. In a year it will outgrow your tank. Maybe even less.
Fourth, aquariums usually do not accept 'stray' sharks and your LFS certainly will not take it back.
As a felkow shark enthusiast I would urge you not to get it. If you truly want a shark, consider a Bamboo, Cat, Coral or Epaulette; these species do not exceed 36-42" in length (usually) and are much less active then Leopards. Another common shark is the Marble, but these do not ship well at all. If you are going to consider it, make sure it is breathing regularly, moving occasionally, and eating well.
Good luck,
Eddi