Can i get whole crabs here? With the backs on them (not blue crabs though)

They periodically have blue crabs! When the season is more demanding. I order 1/2 dozen. The price is reasonable.

No

Where in Sumter can I get that?

No they don't sell crabs

I've never seen crabs there

I dont think you can. Ive never seen any crabs there the many times that ive been there.