Negotiations is a representation of a character's etiquette, manners, bureaucratic know how, diplomatic approach, and a general way with words. Also, diplomatic characters will be able to get a feel for the local laws and customs with a little bit of talk and conversation. Persuasion is the ability to barter, negotiate, make a political impression, and to influence others.
Persuasion can be used for many things: bartering, requesting audience with an important official or citizen, pleading a case before a court, or requesting assistance from a ruler or political group. Successful negotiation means that the character made some progress, although negotiations can only be taken so far before the determining party (such as a gate guard, judge, or ruler) can go no further.
Persuasion can be skill test against a specific target number or an opposed test.