From the Atlantic: Permits. Remember-the government has to get its cut.

http://www.theatlantic.com/national/archive/2011/08/americans-should-be-able-to-sell-stuff-without-a-permit/244250/

Americans Should Be Able to Sell Stuff Without a Permit

"The normal mindset among U.S. officials is that prior permission should be required to sell legal goods to a willing buyer. Kids selling lemonade on the street are shut down. A Missouri man has been fined $90,000 for selling rabbits (he made about $200). In Illinois, an artisan ice cream maker is being shut down for lack of a dairy permit. Manuel Winn was arrested, handcuffed, and booked for selling magazines door-to-door without a permit. A Maryland mother of three was arrested for selling $2 phone cards without a license. Lots of municipalities are going after food trucks. A group of Louisiana monks had to go to court to win the right to sell simple wooden caskets to consumers.

If you read enough of these stories, you'll see the targeted entrepreneurs say the same thing again and again: I just had a good idea and started a business. It never occurred to me that I needed permission. "