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.
Trading goods and services without the use of money is called bartering. Early civilizations relied on this kind of exchange. Even cultures in modern society rely on it. Think of people in prison who commonly trade cigarettes for protection or extra food. For the most part, they don't have cash. So, like people in pre-currency economies, they work with what they have.
The Buy-day (Wheat) Ecological Life Associate summarizes a vision of life in Gezi as follows: "In our world, which is being poisoned and destroyed by consumer culture, we need sustainable and self-operating models of lifestyles, including a barter economy, ecological food production, arts and craftsmanship based on needs, renewable and effective energy use, agricultural models backed by society, permaculture, slow cities, transitional towns, eco-villages, district gardens and secondhand and recycling systems.
Custom - You can also choose to set your own preferred racial settings. Use this option if you are using a custom race. Friendship will still cause the merchant to ignore any racial bias, however the custom settings will not include the built-in exceptions and will not distinguish for merchants located in Solitude. Options: -15% to 15% effect on prices.
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.