Popova bought on the market

Popova bought an elegant dress on the market from an individual entrepreneur and showed it to a friend. The latter told her that in a nearby shop the same dress was much cheaper. Popova went to the market, found an entrepreneur and demanded to return part of the purchase price to her or take the dress back and return the money to her. The entrepreneur refused, and Popova appealed to the legal department of the market administration. What clarifications should she get? What will be the explanation if Popova, when he came home, found poorly processed seams, and the seller refused to take the dress back, referring to the fact that the quality of the treatment of seams is usual for such things made in Turkey?