Some say the Montgomery Ward shopping catalogue is one of the most influential books in US history. It transformed the middle-class way of life in the late 19th and early 20th Centuries. Ward struggled to get people to understand mail order shopping. His prices were so low, people thought there was a catch. Soon, though, this type of retail would improve roads and the postal service. Tim Harford describes how similar dynamics are changing today’s middle-classes in China, with the internet replacing the postal service and e-commerce the new mail order.