India, Feb. 27 -- It happens quietly, often in the middle of the night. A post goes up on a neighbourhood resale group on Facebook-a sleek espresso machine, barely used, is listed for a fraction of its original price. Within minutes, the comments pile up: "Interested!" "Next in line." "DM'd you!" By sunrise, the machine has a new owner, no haggling, no middleman, no storefront.

But more often than not, online resale and buy-nothing groups just have an uncle overestimating the value of his stinky '90s sofa, some lady trying to get rid of ugly crockery, and families expecting full price for an "only used in summer" AC. The trick to making the most of a swap group calls for generosity, community and . strategy. Those who've tried it say it ...