Immoli: At least in the USA. Excluding some things like alcohol, pretty much anyone can sell anything. Don't have to be "certified" or "official" or anything.
JMich: I was under the impression that even a lemonade stand needed a permit. Then again, such knowledge was gained from "The Simpsons" and "According to Jim". Is that not the case?
I'm talking about for selling specific items. A store can sell whatever they want, with few exceptions, but yeah, pretty sure you have to have a permit to open a store. You just don't need a permit to sell toilet paper, paper towels, video games, movies, CDs, frozen pizzas, ice cream, ect.
And you definitely don't need to be certified individually for every single brand.
edit: And then people tend to do garage sales or ebay sales and shit from their house in small quantities without a permit.