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.
Such people are drapers, clothiers, cloth merchants, or dry goods merchants.
Textile Merchant
Walmart....
who is a mercer
A man who sells men's clothing is called a haberdasher and the store is called a haberdashery.
Such people are drapers, clothiers, cloth merchants, or dry goods merchants.
auctioner
You can find information, if Gap sells maternity clothes by looking on their internet site, they will have a range of clothes for sale in all shapes and sizes for women.
A hatter
Ironmonger.
A hotdog vendor
A confectioner.
Draper
It's an old term, probably obsolete by now, but someone who sells fabric is called a mercer.
An agent or representative.
Daniel Studley.
clothier