He wished to discuss a trade dispute that had arisen between the Karemma and the Federation over taxes and fees imposed by the Ferengi Alliance, the intermediary between the two. Hanok told Sisko of the Ferengi charges including those for inspecting cargo for Founders and a tariff to help Tarkalean sheep herders – Ferengi-imposed taxes that had escaped the notice of the Federation Council.
The meeting between Hanok and the Defiant crew was detected by two Jem'Hadar warships who attacked Hanok's ship, which fled into the atmosphere of a nearby class-J gas giant. They did not respond to Hanok's transmission to not flee.
After the Defiant entered the planet's atmosphere to help the Karemma, Hanok was escorted to the mess hall, where Quark told him that the trade dispute was Rom's fault. Hanok was unconvinced and told Quark that "If we survive this, I'll see to it that you never do business in the Gamma Quadrant again."
Later, a Jem'Hadar torpedo impacted into the mess hall near Hanok and Quark, but did not detonate. The two later worked together and successfully defused it, aided in part by Hanok's knowledge of the design; Hanok himself had sold the weapons to the Dominion. When Quark accused him of lying when he claimed to "never sell sub-standard merchandise", Hanok's ironic response was that he should probably offer the Jem'Hadar a refund.
After the Defiant destroyed the Jem'Hadar ships and rescued the Karemma crew, Hanok was brought to Deep Space 9 to await transportation back to Karemma. As he had promised, Quark introduced Hanok to dabo. Hanok later won a substantial amount of money, much to Quark's surprise. (DS9: "Starship Down")
The script for "Starship Down" states the pronunciation of Hanok's name is "HUN-ock". It also describes him and his people as, "tall, thin and elegant in bearing. Although the Karemma are mercantilist by nature, they're classy about it: think fine gem appraiser, not used car salesman. 
Cromwell had difficulties filming in the heavy prosthetics required for the role of Hanok. As he explained, "The makeup was pretty dominating. I don't know how an alien feels about any particular thing, so I just played him as a Human character and tried to handle the makeup." (Star Trek: Deep Space Nine Companion, p.284)