Stall-holders at a bartering market in the central Greek city of Volos, where shoppers use Tem coupons to exchange services or products. Photograph: Despoina Vafeidou /AFP/Getty ImagesIt's been a busy day at the market in downtown Volos. Angeliki Ioanitou has sold a decent quantity of olive oil and soap, while her friend Maria has done good business with her fresh pies.But not a single euro has changed hands – none of the customers on this drizzly Saturday morning has bothered carrying money at all. For many, browsing through the racks of second-hand clothes, electrical appliances and homemade jams, the need to survive means money has been