They might be a ticketing agent, an office clerk, or a scalper.
travel agent
Box office clerk
conductor
Ticket seller.
A ticket vendor is a person who sells tickets -.-
You would call it a ticket office or a ticket broker.
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