"beginner" doesnt mean "small", but sadly, as mike22cha said, some people think it does when they go out and buy fish and such ><. I mean sure, you will get those people who buy it because they like sharks, think its cool to have a shark, or are just plain dumb and wanna see how much they can cram in their tank. All of those people usually have no knowledge about taking care of sharks.
Thats why I am kinda glad sharks have the stigma of "hard to keep" saltwater, even though, from my experience, they are very easy to care for, except for their size and tank requirements upon that. Im glad alot of sites and stores say sharks require "expert" care to be kept in captivity.
This is SO True.
Think about the Fact that many sites list the Nurse Shark(Ginglymostoma cirratum) - as a "beginner" shark. Yet these sharks will eventually reach over 250 lbs, and at least 8-10 ft long. Most Aquarists don't have the room or finances to keep one of these shark for it's entire life(up to 30-40 yrs). Yet, They are called "beginner" sharks - because of their small birth size(10-12") and incredibly hardy nature makes them relatively easy to keep (at least for the 1st year). Nurse are incredibly tough sharks - even capable of tolerating relatively poor water conditions. But this is really a species that should only be kept by someone with room and finances for a swimming pool size shark lagoon (at least 20,000 gallons) - which will allow them to keep the shark for life.
But while a Nurse isn't very practical, a Brown-banded Bamboo is. A 500 or even 1,000 gallon pond is alot easier to build & take care of than a 20,000 gallon Swimming pool size shark lagoon.