The certificates also help prevent fraud. Some companies were found to have falsified income statements in order to give tax breaks to upper-level management while simultaneously increasing tax costs for workers lower on the ladder, Huang said.

But tax-paid certificates are not enough to solve the mystery. Corporate and individual income taxes accounted for 28 percent of China's 6.3 trillion overall tax revenue last year, while the rest came from indirect taxes, mostly value-added taxes and consumer taxes. These taxes are even harder for some taxpayers to understand.

Many Chinese consumers are not aware that they are paying taxes when they pay for goods and services. Three of these taxes - value-added taxes, business taxes and consumer taxes, are not mentioned on price tags or invoices, Su said.

A typical consumer pays 13 to 17 percent extra for every product he buys that has an attached value-added tax, according to Su. "However, the consumer sees only the price tag," he added.

In addition, consumers pay 3 to 20 percent extra for services with business taxes attached, according to Su. Consumable goods and goods that produce a lot of waste, such as chopsticks and cars, can be taxed from 3 to 56 percent of their price, Su added.

Officials from the State Administration of Taxation say the greatest difficulty is that tax authorities do not have accurate income information for all taxpayers. To get this information requires a coordinated effort between different government departments and agencies.

Most income taxes are collected from middle- and low-income workers because it is easier to measure their incomes, according to Zhang Bin, a tax researcher from the Chinese Academy of Social Sciences.

Income taxes are designed to narrow wealth gaps, but in reality, middle- and low-income earners are the most heavily taxed, Zhang said. The income tax threshold needs to be raised to make it more fair, Zhang added.

China's income tax threshold will be raised from 2,000 yuan to more than 2,500 yuan, said Li Fei, deputy director of the Legislative Affairs Commission of the National People's Congress (NPC) Standing Committee. The NPC is China's top legislative body.

The State Council, or China's cabinet, approved a plan to raise the threshold in early March. However, the plan has yet to be delivered to the NPC Standing Committee for review, Li said at a press conference on March 10.

But Chinese citizen Liu Zuo does not believe that raising the income threshold is the solution. Value-added taxes on food, medicine, clothes and other daily necessities should be cut instead, he said.

"When people consume in supermarkets and restaurants, they pay a lot in taxes. Many of them are not even aware of it. This is what burdens low-income families in real life," Liu said.