who is a mercer
Someone who sells clothes is typically called a "clothing retailer" or "apparel retailer." If they operate a specific store, they may also be referred to as a "boutique owner" or "store owner." In a more general sense, they can be called a "salesperson" or "sales associate" in the context of a clothing store.
A florist.
jeweler
A glomber
Someone who works in textiles is commonly referred to as a textile designer or textile worker.
auctioner
A hatter
Ironmonger.
A confectioner.
Draper
A hotdog vendor
It's an old term, probably obsolete by now, but someone who sells fabric is called a mercer.
An agent or representative.
clothier
Daniel Studley.
A confectioner is someone who makes and sells candies and sweets. A chocolatier is someone who specifically makes and sells chocolate.