Kautilya's Arthashastra 2.21.28

2.21.28

tena pradeśena rājā śulkādhyakṣasya sārthapramāṇam upadiśet sarvajñakhyāpanārtham //

Or he may send to the king a spy in the guise of a trader with information as to the quantity and quality of the merchandise. (Having received this information,) the king shall in turn send it to the superintendent of tolls in view of exhibiting the king's omniscient power. The superintendent shall tell the merchants (in question) that such and such a merchant has brought such and such amount of superior or inferior merchandise, which none can possibly hide, and that that information is due to the omniscient power of the king.