Xu Shiyou markets his balloons in Harbin, Heilongjiang province.Liu Yang / For China Daily

"In the past 10 days, I have been able to earn more than 100 yuan ($14.50) a day. During the three-day Tomb Sweeping Day holiday, I sold more than 100 balloons every day, which brought me more than 200 yuan," he said.

Xu needs the money to buy medicine for his 72-year-old wife, who has heart disease, high blood pressure and kidney stones. "She needs to take the medicine long term and it costs about 1,000 yuan a month," he said. "However, if her condition becomes serious and she has to got to hospital, the cost would be astronomical for us."

In order to save money, Xu buys the cheapest medicine he can for his own pulmonary emphysema, tracheitis and low blood pressure - only spending about 100 yuan per month.

In 2011, the couple moved to Harbin from a village in Xuzhou, Jiangsu province, because they believed it would be easier to earn money in the metropolis. They now live in the same small house as their daughter, who doesn't have a steady job.

At first, Xu made money by collecting materials to be recycled. "But I became too old to carry those heavy materials, so I began to sell balloons around shopping malls and night markets in 2013," he said.

For a while he would earn no more than 50 yuan a day selling balloons, until a chance encounter that led to his story becoming widely circulated on social media,

"People have told me that they have come from far and wide just to buy my balloons after learning of my story through WeChat - some have even left me more money than the price of the balloon," Xu said.

"I remember talking to a young girl who looked like a college student at the end of March, she must have been the one who told others my story. I want to say thank you to her for her help, but I haven't seen her since."

Despite leaving home at 8 am every day and standing on the street for up to 12 hours, the smile rarely leaves Xu's face. He enjoys paying his own way, and refuses any help from his children.

"We have two sons and two daughters, but they are not well-off," he said. "Since I have the ability to be self-reliant, I don't want to become a burden on them."

Xu said the happiest thing in his life now is eating dinner with his wife each evening. "Every day my wife will wait for me to have dinner together - in the daytime, we worry about each other, but we can chat over dinner. It is the most wonderful time for us," he said. "We have been married for nearly 60 years and my wife has dedicated her most beautiful years to our family. Therefore, I should and will take care of her."

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