Guangzhou delivery vehicle driver Zhang Liang watches on warily as more graduates, former factory workers and other jobseekers join him plying their trade on the roads.“The streets are flooded with delivery drivers and payouts per order have plummeted,” Zhang said. “To make what we earned last year, we have to stay on the road longer and ride faster, leading to a sharp rise in traffic accidents among us.”Official estimates put the nation’s flexible workforce at nearly 300 million, most of whom...