This basic mechanism of an indirect tax collected by private merchants supervised by government officials endured to the mid-20th century.
Liu had already proved his worth by using impressed labor to dredge the long silted-over canal connecting the Huai and Yellow rivers; this project lowered transport costs, relieved food shortages, and increased tax revenues with little government investment.
This monopoly price was an indirect tax which was reliably collected in advance without having to control the areas where the salt was consumed.
[1] The commission formed to oversee the new scheme was headed by the salt commissioner (yantie shi), a financial specialist, which was uncharacteristic of the Tang unspecialized political administration.
The distribution by merchants ensured the effects of the policy penetrated into areas where the central government had limited authority.