Trade in Skyrim is oversimplified and uninteresting. A particular type of merchant always has the same amount of gold and offers you the exact same prices as the same type of merchant in another part of the country. Merchants in small towns differ very little from those in the larger cities, and the only factors that affect price are your speech skill and any barter enchantments you might have.
By default this option is turned off. When you load the mod menu, the value you see displayed is the setting currently in use in your game. The vanilla value is 2.0, so any other number indicates that another mod is already changing this setting. If you decide to turn this option on, than the settings from Trade & Barter will overwrite any changes to this value made by other mods. If at any time you wish to revert the settings back to those made by another mod, simply toggle off this option and reload your game. You will need to reload your game before the changes from Trade & Barter are fully canceled out.
Barter, the direct exchange of goods or services—without an intervening medium of exchange or money—either according to established rates of exchange or by bargaining. It is considered the oldest form of commerce. Barter is common among traditional societies, particularly in those communities with some developed form of market. Goods may be bartered within a group as well as between groups, although gift exchange probably accounts for most intragroup trade, particularly in small and relatively simple societies. Where barter and gift exchange coexist, the simple barter of ordinary household items or food is distinguished from ceremonial exchange (such as a potlatch), which serves purposes other than purely economic ones.
In a small economy where individuals specialize in trades, they may find the process of setting up a centralized currency and maintaining it an unnecessary burden in order to trade. One option may be to use a commodity to exchange value between parties that want to trade goods or services and this is why gold and silver have been useful forms of currency in many cultures and times. Another option may be to use a barter system to trade. 

He would have heard of channels and sandbanks, of natural features of the land useful for sea-marks, of villages and tribes and modes of barter and precautions to take: with the instructive tales about native chiefs dyed more or less blue, whose character for greediness, ferocity, or amiability must have been expounded to him with that capacity for vivid language which seems joined naturally to the shadiness of moral character and recklessness of disposition. 
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