In a report released in June, Xianyu said 300,000 blind box collectors made deals on its platform last year, up 320 percent from 2017. The most popular box is the "hidden version" of Pop Mart's Satyr Rory Sweet Christmas series, which is listed at 2,350 yuan, nearly 40 times its original price in vending machines.

Wen has jumped out of the "hole", having sold most of his collection on Xianyu in 2017 and 2018. He earned 45,000 yuan from dolls he bought for 20,000 yuan.

Anyone can be a blind box expert if they put in the effort and money, he said, but it costs too much time and energy, adding that he once waited for hours beside a vending machine for the chance to get the "hidden version" of a Sonny Angel doll.

"The time and energy you exert doesn't get paid back, that's the main reason why I quit," Wen explained.

Members of Generation Z, those born after 1995, account for most of the 200,000 consumers who spent more than 20,000 yuan last year collecting blind boxes, Tmall said in a report released in August.