"Great Merchants" provide the goods and services civilizations need to survive. They import food, medicines, and luxuries, and they export a civilization's manufactured goods. They provide the financing needed for great works to be accomplished. They create a civilization's wealth.
Strategy
Besides constructing the special Customs House improvement which, when worked, produces loads of Gold, the Great Merchant can also journey to a city-state and perform a "trade mission" which produces gobs of Gold and gains many points of Influence with the city-state. The Great Merchant is expended when used in either of these ways.
Again, you have the choice to use it for a long-term boost of the Gold production of one city (choose this city well), or use its unique ability to get a large one-time boost of Gold and Influence with a City-state. Note that the Trade mission may sometimes prove dangerous, especially if the City-state is far away.
Generates bonus Influence from Trade Missions, scaling based on distance from the Capital
May be expended in the territory of another Major Civilization to conduct a Diplomatic Mission, providing a burst of Influence with every City-State allied to that civ
Custom Houses created by Utusan claim adjacent Coastal tiles.
If inside the territory of a city-state, nearby combat units may pressure the City-State into allowing tribute much more effectively. This can be repeated with each city-state further away from the Capital than the last.