At the same stall, a man at his late 20s was sitting on a wooden bench, carefully checking some old postcards with a flashlight. He then picked several from the pile, bargained with the owner, and paid about 12 yuan ($1.70) for them.

The stall sells secondhand daily items from the 1980s and '90s, such as large vacuum flasks that were once must-haves for almost every Chinese family, old banknotes, and pagers and watches.

Elsewhere in the market, Liu Qingli and her boyfriend set up a stall to sell the badges they bought while traveling abroad.

"The more I travel, the more I collect. But it was only recently, when I was about to move house, that I realized what a large collection I had. So I decided to sell parts of it to save some space and see if I could make some money," Liu said.

Although Wang Jiashuang, a 28-year-old white-collar worker, has never been to the market, she also has some experience of selling secondhand goods.

When she was about to graduate from university a few years ago, she and her friends set up a stall on their campus.

Wang, who graduated from Renmin University of China, said, "During the graduation season, the university designates an area where students can set up stalls to sell anything they don't want to take home."

She said a wide variety of goods is available, ranging from books, stationery and toys to clothing and bed linen. "Basically, you can sell anything you want."

The university flea market usually lasts for about a week. The variety of items and low prices attract not only students, but also many nearby residents.

"There were five or six of us, and one of us had a rather eye-catching tent. Our sales situation was pretty good," Wang said. "After three days, we went out for a big meal with the money we had earned."

Liu, who set up the badges stall at the ghost market, said making money is just one aspect of selling items there.

"It also gives me a chance to meet and talk to people with the same interests. But it's since become harder and harder to find anywhere that will allow us to set up a stall. The ghost market is the only place I can think of," she added.

Ding, the amateur collector, said there used to be three or four more flea markets in Beijing. "But the Daliushu venue is probably the last that can be called a true ghost market."

Li Hongyu, an urban planning researcher from the Chinese Academy of Social Sciences, said the number of open markets in Beijing has fallen in recent years because of continuous development and planning changes. "A larger open-air market involves urban management, such as traffic diversions, relations with nearby residents, sanitation, social security, and even whether use of the land complies with the planned design," Li said.

But she added that such markets should be an important component of urban life.

"On one hand, a market can meet buyers' needs in a more convenient and cheaper way, filling a gap that a large shopping mall is not able to. On the other hand, it also provides a way for the vendors to earn a living."

Li cited the example of seasonal or temporary farmers' markets overseas, where buyers can purchase directly from producers but only in regulated areas during set periods of time.