But their success has also drawn scrutiny, with officials in both China and Australia examining whether they are paying required taxes and complying with other regulations.

The business is in many ways a byproduct of China’s huge interest in a different kind of Australian product: international education, considered one of the nation’s top exports, worth $15 billion a year. Nearly a third of the 450,000 foreign students in Australia are from China, and the figure is growing.

Peter Cai, a fellow at the Lowy Institute, a think tank in Sydney, said the students had become a powerful force helping Australian products break into China. “Just through the daigou’s own personal networks, they enable a new market for a small- and medium-sized business in Australia,” he said.

“I think we’re almost entering a new phase of the China-Australia economic relationship” requiring greater understanding of the Chinese market, he added, and the students provide that understanding.

Chinese purchasing agents first appeared in Europe, buying and shipping luxury goods like handbags for China’s growing middle class. But the trade has shifted to Australia in recent years as the Chinese student population in Australia has expanded and consumers in China have grown more anxious about food and product safety.

Worries over infant formula, for example, surged in 2008 when six babies died and more than 300,000 children fell ill from drinking Chinese milk products that had been tainted with melamine, a toxic chemical. Many in China turned to imported milk powder in response, but reports of distributors or retailers adulterating it with Chinese formula prompted consumers to directly seek supplies from overseas.