Variable Merchant Gold - Adds more gold to select merchants. Merchants in major cities will no longer have the same amount of gold as their small-town counterparts. There are three levels with increasingly greater difference between the gold amounts for city & small town merchants. Personally, I would recommend leaving the Base Merchant Gold at vanilla values and choosing one of the Variable settings instead. You can stack the Variable settings by selecting multiple options in order to get even greater increases in merchant gold, but I really don't recommend doing this as I haven't balanced the values with this intention.
Default - These are preselected values. See the Race Relationships chart in Images to view what the default race settings are. There are also some locational differences. As the cosmopolitan capital, residents of Solitude express less racism than elsewhere in Skyrim. However, Nords who are residents of Windhelm or part of the Stormcloak faction express stronger racism. I've also built several exceptions into the default settings to reflect individual character traits present within the game. Also, your personal relationship with a merchant is more important than any general feelings they may have toward your race and will override any general racial bias.
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.