Nintendo is selling refurbished 3DS and DSi XL systems directly on its website. "Authentic Nintendo Refurbished Products" are, according to the manufacturer, "the only refurbished products in the market that have been cleaned, tested, and inspected to meet Nintendo's high standards." They also come with a one year warranty.
As Ars Technica points out, these refurbished systems not only offer a better guarantee than used systems sold at GameStop, it is undercutting the retailer as well. A new 3DS costs $170, while a used one at GameStop costs $160. The Nintendo direct system is $130, a substantial savings over both alternate options.
The selection offered by Nintendo is rather limited, however. Their official store does not include Wii, Wii U, or 3DS XL systems.