Reselling Retail Items at a Flea Market?

I was walking through a flea market in Fort Wayne, Indiana this past week and noticed that one lady had a large 'booth' in the flea market. Her booth looked like a candy store. I spoke to her for about 10 minutes. Apparently, she drives to Sam's or Walmart (but I don't know this for sure) and purchases items that are on sale (like Hershey Bars and Life Savers) adds about 50 cents to the price she paid and resells them at the Flea Market. Can you actually purchase an item retail and resell them to the public? I thought about this while I was driving from the flea market.