To make things worse, Chen's father insisted she take the cure-all he bought from his club, and took her to see the "experts" for treatment instead of taking her to hospital for further rehabilitation.

After Chen learned how his mother had fallen victim to the fraudsters, he was shocked. They provided her with free physical examinations and helped her carry things she bought at markets.

"They even came to her home to help with cleaning and cooking, and became my mother's 'sons' and 'daughters' to win her trust," he said. "They're so sophisticated that simply telling my parents to be careful didn't help. Old people are easily brainwashed by the people selling health products."

Despite numerous attempts, he could not shake his father's belief in the dubious health products or stop him from going to the club.

Frustrated, he decided to try his best to help others. In December, he opened an account named "Umbrella Utopia" on WeChat, providing advice on how to protect the rights of the elderly when they are duped by dubious health products.

It is a widespread problem.

In June, the daughter of an 85-year-old retired professor in Xianyang, Shaanxi province, called police to stop her father from buying a herbal mix claimed to be a special ancient prescription that can heal heart problems.

She told the local newspaper, Huashang Daily, that there was no manufacturer's name or serial numbers on the packaging, and that her father had spent more than 100,000 yuan on such "health products" since 2009 and refused to listen to her warnings.

In November 2016, a 74-year-old woman died during a health lecture after spending 320,000 yuan in three years on various health products and refusing to go to hospital when she became ill, China Central Television reported.

Posts about how to dissuade parents from buying dubious health products are all over the internet. On Zhihu, a popular Chinese Q&A website, a post along those lines has been viewed more than 1.5 million times and has generated more than 300 answers.

Zhang Xin, an associate professor of psychology at Peking University, said in one reply that the elderly are prone to being duped because their source memory, which helps people recall the source of information and judge whether it is reliable, is declining. So when the elderly are told repetitively some products are good, the idea will be inked into their minds with a high degree of certainty.