A shopping district in Beijing. At the heart of China’s retail economy is a system of mobile payments that is so cheap and simple it has allowed most people to ditch cash without ever having used credit or debit cards. Photograph: Mark R Cristino/EPA We were admiring a large, yoke-back armchair in the Ming style when my companion nodded towards the showroom manager who was looking back at us from behind a red sandalwood table with an upturned flange. “I’ve told him that you’re interested in Chinese culture and that you are very knowledgeable about it. I said this is…