Buying used books from the store has brought more unexpected bonuses to Shen: small mementos it often sends her when it dispatches books to her. Once she bought a novel by the Japanese author Keigo Higashino and received a message sent via the mini-program from its previous owner saying the story was fascinating and that she hoped she would enjoy it, she says.

"That message gave me a very warm feeling, and because of it I read the book more attentively than I would have otherwise, trying not to miss any of the detail."

However, for Shen, 27, a clerk with the Bank of China, the most appealing feature is that these books are so cheap. Since September last year she has bought more than 500 books from Duo Zhua Yu mostly at a discount of 60 percent, spending a total of 7,000 yuan. She has also sold more than 200 books to the store at a discount of about 80 percent.

"I always buy social science books there. The most popular ones are hard to find, and sometimes when I'm finished reading I sell them back to the store."