The following description is from dminoz's "Daily Imperialist". (Authorship and copyright not certain, and his e-mail seems to be dead; if he or anyone else claiming authorship thinks this should not be here, let us know.) :
- Treat the Merchant with reverence: this unit makes you money. It also greatly, though indirectly, help you in the execution of your diplomatic policies.
- The Merchant demands a sizable investment to make things worthwhile. Take this into account! It's unproductive to spend $1,000 on an embassy and then $500 on a Merchant, then find out you have only enough cash left for a single land purchase.
- If you use the Merchant wisely, you can expect to recoup your investment in land within twenty turns, possibly quicker if relations between you and the original owner of the purchased land are fairly cordial. Try to complete all purchases within one territory before moving the Merchant to another Tribe or Minor Nation. It's a good idea to purchase several different types of resource producing land. If, turn after turn, you buy three commodities from someone, that's three trades, and a threefold improvement in your diplomatic relationship. If you buy three units of a single commodity, it only counts as a single trade, and it will take three times as long to assimilate this particular trading partner into your empire.
- Once all the Minor Nations are gone and you've bought all the interesting plots of land in your colonies, there is no further use for the Merchant. However, civilian units don't require upkeep, so don't disband a unit until you're absolutely sure there's nothing more for him to do.