Shark Fin Vendor is a character who owns a Shark Fin booth on Main Street. If you talk to him, he'll give you a free Shark Fin. You do not need to talk to the Shark Fin Vendor when completing Shark Tooth Island.
The Shark Fin Vendor is really friendly and will give you a free shark fin after you talk to him.
The Shark Fin Vendor has yellow skin and brown hair. He's wearing a blue and white hat along with a blue shark on it with a matching shirt. He's also wearing blue pants and has a grey shark fin on his back.
Because the Shark Fin is an optional item, the Shark Fin Salesman may simply be ignored by your Poptropican.