To me it depends quite a bit on what species of shark was involved. Not all are endangered and many are legally caught (the entire fish, not just for the fins). A three foot shark doesn't provide a heck of a lot of fin, so the fins may simply have been cut off for display purposes. If the shark was a threatened or endangered species, I'd really have concerns. If the shark had been caught, de-finned and the carcass thrown back into the water, I'd also have REALLY big concerns. Our local market used to sell shark steaks (mako mostly) and as far as I knew it was legal take.
Personally I wouldn't eat shark anyway. Bioaccumulation of nasty stuff in their tissues for the high order pelagic feeders and a concern for bottom feeders getting high levels of nasty stuff from the sediments and lower order species feeding there would stop me.