Someone who sells sewing items might be a seamstress, a needlworker, dressmaker, couturier, garment maker, sewist, artisan, craft-maker, or vendor.
auctioner
A hatter
Ironmonger.
A confectioner.
Draper
A hotdog vendor
Someone who sews on a machine is commonly referred to as a "sewing machine operator." This person typically operates and manages sewing machines to create or alter garments and other fabric items. In some contexts, they may also be called a "seamstress" or "tailor," depending on their specific role and skills.
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.