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.