A person who sells donuts is typically called a "donut seller" or "donut vendor." If they operate a dedicated shop, they might also be referred to as a "donut shop owner" or "baker," depending on their role in the production and sale of the donuts.
Dunkn Donuts sells double glazed donuts. Dunkin Donuts also sells other flavors and varieties of donuts as well, such as maple glazed, donut holes, and etc.
An author is a person who writes and sells books.
The person who sells drink is known as sellsmen
baker
You call a person who sells flowers a (Florist)
A bookie. Droll. You could call that person a bookseller or shopkeeper.
A person who sells ship supplies is called a chandler
A person who sells jewels is called a jeweler.
fishmonger
A chandler.
A butcher.
A florist.