The measure that determines liability for carrying out paper is equivalent to that which is used to write a tax receipt. And one who carries out a tax receipt itself on is liable.
In ancient times, a significant portion of state revenue came from tariffs, which were typically levied at borders, crossings, bridges, and major thoroughfares. For many years, central authorities leased the right to collect state taxes to individuals. These tax collectors often raised taxes beyond the official rate of taxation or levied taxes on items that were actually exempt from taxes to increase their own revenues. There were even self-appointed tax collectors whose authority ranged from semiofficial to non-existent. Due to the irregularities with regard to taxes, some people made private arrangements with the collectors. Through fixed payments or due to good personal relations, they received exemptions from taxes. A tax receipt was a kind of certificate stating that a tax collector had exempted a merchant or traveler from paying a tax. Since these exemptions were distributed on a personal basis, they were occasionally used to demonstrate to a different tax collector that the bearer was trusted by the tax authorities, in the hope of gaining consideration with regard to his taxes.
Thus, we find the following in the Gemara:
The Sages taught in a Tosefta: One who carries out a tax receipt on before he has shown it to the tax collector, and he still needs it, is liable for carrying out on. Once he has shown it to the tax collector he is exempt, as it has no significance. Rabbi Yehuda says: Even once he has shown it to the tax collector he is liable because there will be a time when he needs it.
Abayye said: There is a practical difference between their opinions with regard to tax runners.
Occasionally, the tax collectors send inspectors after those who already passed the tax audit in order to verify that they indeed paid. In that case, even though one already showed it to the original tax collector, he will be required to produce it again.
Rava said: There is a practical difference between their opinions with regard to a senior tax collector and a junior tax collector.
Sometimes, when the first tax collector that one encounters is a minor official, he will need to keep the receipt with him and produce it if he encounters a more senior official.
Rav Ashi said: There is a difference between them even in a case where there is just one tax collector. Nevertheless, it is to his advantage to keep it in his possession because he needs it to show it to a second tax collector whom he may encounter in the future, as he says to him: Look, I am a man trusted by the tax collector.
According to this opinion, the document in his possession proves that he is on good terms with the tax authorities.