THE first daigou, meaning someone who makes purchases on another’s behalf, were Chinese students studying abroad, who hauled desirable products home on behalf of family and friends. Adding a commission helped them pay their tuition fees. The spread of social-networking apps such as WeChat, China’s most popular, brought the business online. Daigou could then offer their services to friends of friends, and promote items they thought might appeal to their network. But whereas daigou in America and Europe procure mainly luxury goods for their customers—a function of high Chinese tariffs—in Australia they buy mainly vitamins, food and beauty products. And whereas luxury brands see daigou as a menace, undercutting sales in China, Australian firms have come to embrace them.

There are perhaps 50,000 daigou, stalking the aisles of Australian shops and periodically stripping them bare. The small fry alone post 60,000 parcels to China every day. The biggest have grown into organised export businesses which funnel goods through China’s free-trade zones. Express delivery services to China have proliferated, and some 1,500 stores in Australia cater mainly to daigou. One such chain, AuMake, recently listed on the Australian Securities Exchange. Its bilingual sales staff can arrange for a purchase to be posted to China as soon as it has been rung up.

The appeal for the customers is simple: the products daigou post are guaranteed to be genuine. After Chinese firms were found to have been selling contaminated milk powder in 2008, many anxious Chinese parents turned to foreign brands. But websites peddling foreign goods are riddled with counterfeits, while Chinese shops charge a fortune for the real thing.

The odd sales channel works for companies, too. Daigou allow young Australian firms to build their brands in China much more cheaply and easily than if they tried to market their products directly, argues Keong Chan, the chairman of AuMake. A firm called the a2 Milk Company doubled its profit in the year to June thanks to soaring Chinese demand. Daigou account for more of those sales than Chinese retailers or e-commerce sites, according to Peter Nathan, who heads its Asia-Pacific unit. Businesses fall over themselves to win the favour of the most influential daigou, offering discounts and Chinese marketing materials. “It’s like having a 50,000-strong sales force,” says Andrew Cohen, chief executive of Bellamy’s, a listed manufacturer of infant formula.

Bellamy’s learned the hard way. It used to worry about entrusting so important a market to squads of anonymous intermediaries. Daigou had earned a bad press in Australia for creating shortages of certain goods and for failing to pay tax on their commissions. Worse, the Chinese authorities began talking last year about demanding import duties on personal packages, a move that the firm feared might undermine sales through daigou.

So Bellamy’s decided to funnel its wares to Chinese retailers and e-tailers, who in turn offered big discounts to customers, undercutting the daigou. This approach backfired completely, as daigou abandoned Bellamy’s products. Sales plunged. The firm’s share price collapsed; heads rolled. Bellamy’s recently cut back sales to other distributors, restoring daigou to prime position once again.