Cao Jinghua became a watermelon farmer at his 20s and has been a verification expert for more than two decades.

"My previous experience as a melon farmer laid a good foundation for me to work as a verification expert," he said. "I spend more than half the year outside selecting watermelons."

Usually, several days after Spring Festival, he travels to Yunnan province or the Guangxi Zhuang autonomous region near Myanmar and Vietnam to select melons, he said. And then, as the fruit ripens at different times, he gradually makes his way north.

Currently, in the main watermelon-producing areas across the country, verification experts have become sought-after resources. While a few have been around for decades, they are now in short supply.

"During the watermelon trading period, when large quantities of melons are involved and cutting great numbers open is not feasible, professional verification experts are needed to standardize and control the ripeness and quality," said Li Junhui, a fruit supplier with 16 years of experience.

In every watermelon harvest season since 2018, he has hired multiple verification experts to help him select which melons are ready.

"Commercial watermelons generally need to reach 80 percent of ripeness, because there is a shelf life for later sales," he said. "Watermelons that are either too ripe or not ripe enough need to be sorted out. Melons with seeds, hollow parts or deformities are not acceptable. Identification of these require the professional expertise of verification experts.

For Cao Jinghua, listening to the watermelons is the most important skill the experts possess.

"The level of ripeness — whether the flesh is crisp or sandy — can be heard immediately," he said.

Melons of different ripeness levels have distinct vibration frequencies when thumped, he said. Hollow watermelons produce a dull sound, while solid watermelons produce a crisp sound. Immature watermelons often have a clear, lower-frequency sound.

Additionally, verification experts must rapidly assign grades to watermelons based on touch, size, shape, color and pattern. Arranging the melons for long-distance transport to ensure they are not damaged is also a technical skill.

"The top and bottom of a melon is the hardest and relatively more resistant, while the middle part is easily flattened if not placed properly. This can lead to the watermelon being crushed," he said.

During the peak period of watermelon production, verification experts may need to work more than 10 hours a day, inspecting tens of thousands of kilograms of watermelons, he said. "Each expert can verify approximately 4,000 watermelons a day, earning around 3,000 yuan, and during the busiest seasons, they can earn up to 6,000 yuan."

Liu Lanlan, a researcher at the Institute of Journalism and Communication at the Henan Academy of Social Sciences, said that professional verification experts are an example of a new market emerging from the national demand for quality. New professions have appeared that reflect a new trend of detailed professional development.

"The verification profession is in a rapid growth phase," she said. "It currently lacks industry standards for evaluating and certifying a person's skills and experience. So it requires more attention and support from government departments, as well as from inside the industry, to accelerate the improvement of professional standards and systems for training, rights protection and transparent compensation. These are needed for the long-term stable development of the verification expert profession."