Managed to get me some shark teeth at last. Trading 9 for a "human face":
He takes the teeth and leads to an underwater dune, excavating out a rebreather mask. It's actually really nice, but you suppose he doesn't need it for anything.
You found: rebreather mask
If you try to trade without having enough (or any) teeth in your inventory:
He sings a few piteous notes before sending you on your way. Apparently you didn't have enough teeth.
27 for "something about teeth and skin":
He carefully counts over the teeth and leads you to a buried sheet of what proves to be shark skin. It's really slick, but the scales are sharp enough they could probably take your finger off.
You found: cured shark hide
My guess is that fancy hat is a crown.