Sisko learns about an unsanctioned 6% tariff
A tariff was a tax levied by a government upon goods which were imported to or exported from their territory.
In 2372 the Ferengi imposed a six percent tariff on Karemman woolen goods. They claimed they did so in order to offset the "lost income of Tarkalean sheep herders", but Karemman Minister Hanok was skeptical of such a claim. (DS9: "Starship Down")
In 2381, tariffs on Ferengi exports were among the terms of their pending Federation membership application. (LD: "Parth Ferengi's Heart Place")