HONG KONG—For 15 years, Cui Haifeng worked in China's manufacturing industry, stitching together leather to make soccer balls before working her way up to warehouse manager at a wood-flooring factory.

Last month the coal miner's daughter traded a past of factory uniforms for a blouse and skirt, training as a customer-service representative for a life insurer in Guangzhou, southern China's largest city.

The...