At any given moment, millions of articles of clothing are coursing through ThredUp's logistics behemoth. Founded 10 years ago, the company will send you an empty bag for you to fill with clothes that you want to cash in on. Then they'll take them off of your hands to photograph, price, and ultimately sell online -- after which, of course, you pocket some consignment money.

“The source of all of that amazing product are the closets across America. It turns out that people buy a lot of stuff, and even when they don't need to buy more, they buy more," said Anthony Marino, ThredUp's president (and formerly its CMO). "If you look at some recent statistics, in the United States, people buy on average 65 to 70 new items every year, and they wear them maybe 6 or 7 times and then never again.”

Selling stuff through ThredUp, Anthony says, users can both experience the "life-changing magic of tidying up" so astutely promoted by Marie Kondo -- and feel like they're doing their part to reduce waste.