SHANGHAI — To begin to comprehend China’s vast underground economy, one need only visit this city’s major transportation depots and watch as peddlers openly hawk fake receipts.

“Receipts! Receipts!” calls out a woman in her 30s to passers-by as her two children play near the city’s south train station. “We sell all types of receipts.”

Buyers use them to evade taxes and defraud employers. And in a country rife with corruption, they are the grease for schemes to bribe officials and business partners. Making them and using them is illegal in China. Some people have been executed for the crime. But demand is so strong that a surprising amount of deal-making takes place out in public.

It is so pervasive that auditors at multinational corporations are also being duped. The British pharmaceutical company GlaxoSmithKline is still trying to figure out how four senior executives at its China operation were able to submit fake receipts to embezzle millions of dollars over the last six years. Police officials say that some of the cash was used to create a slush fund to bribe doctors, hospitals and government officials.