Finding the perfect dress for my rehearsal dinner was easy; learning that it was sold out was hard. But that wouldn’t stop me. As I scoured Google for the Renata Sheath from BHLDN — an embroidered, beaded dress with an illusion neckline and low back — I found myself someplace unexpected: Facebook. Specifically, a Buy-Sell-Trade (BST) group dedicated to Anthropologie’s wedding line. Unfamiliar with groups like these, I poked around a bit. Soon enough, I’d joined countless others: Anthropologie, Free People, ModCloth, Madewell, Lululemon. I became fascinated by them. Most groups are private, and some are secret. Many have shockingly strict rules. (I ended up getting kicked out of one, in fact. More on that later.) People have been using BST groups for years. But when Facebook added the “sell” button as a feature in 2015, it streamlined the process for buying and selling items, and created a whole new world for shoppers. Several of the larger apparel groups, including the Lululemon one, have over 50,000 members. Some designer handbag and shoe brands also have sizable communities. The largest Louis Vuitton BST group has over 130,000 members, while the largest Yeezy BST group has almost 190,000. Read more at Racked.