"When we look at this, just like a library, and compile these elements from various sources, these very items demonstrate that across different dynasties … they all represent a unified transmission of Chinese culture and civilization," he said.

"We believe these types of books are meant for cultural dissemination and are integral to the preservation of traditional Chinese culture. While they have also contributed to the printing industry flourishing, their purpose isn't for mass public reading."

In the more than two decades Sun has run Kongfuzi, he has observed that the online and offline book markets are closely connected.

Many book collectors trade with each other, whether online or offline. They also spend a lot of time offline discussing and "authenticating" books.

For instance, Liu, the book enthusiast, dedicates a lot of time to book hunting in different markets across Beijing and meeting friends through books.

Zhang, the seller, said when he was younger he would search for interesting books on Thursday night and early Saturday morning at Panjiayuan market in the capital's Chaoyang district.

Being surrounded by books is a haven for bibliophiles, and the friends they've made through books are an integral part of their social circle.

"What we're trying to do is to make more books available so more interested readers can see them," said Sun. "What you can buy with money isn't necessarily what you'll like; developing genuine appreciation for something takes years of dedication."