Negotiation

Inspiration
Thanks go to Rich Burlew, of Giant In the Playground. His revamp of the Diplomacy skill is essentially what I'm using here, with minor modifications.

Explanation
There was a lot wrong with the old Diplomacy skill. Fixed (and low) DCs combined with a pile of synergy bonuses and vague definitions of what effect being "Indifferent" really had made for a skill rife with problems. As Mr. Burlew pointed out, while Diplomacy attempted to give players a mechanic for influencing NPCs, it required so much DM fiat to adjudicate correctly that it might as well have not been there.

So, we replace it with Negotiation. Here's how it works:

Use
This skill is used to determine whether or not an NPC accepts a player's proposal. This can be a bargain the player is offering, a threat, an exchange, or even a seduction.

To use this skill, a player must parley with the NPC, or group of NPCs. Over the course of this parley, the player makes some kind of offer to the NPC. The player must not be attacking the NPC (but may be engaged in combat, either taking no offensive action against the NPC or attacking someone else) and must be able to speak the NPC's language. Use of this skill takes at least a minute, and in some cases, may take significantly longer. A player may attempt to negotiate as a full-round action, but he takes a -10 penalty to the attempt.

The base DC of a Negotiation check is equal to 15 + the target's hit dice + the target's WIS modifier. The check DC is modified by the target's attitude towards the player and by the risk/reward benefit of the player's proposal.

Attitude
An NPC who is hostile to a player is going to be less inclined to accept a player's offer than if he were friendly. Modify the DC as follows:

A creature's attitude may be considered "Fanatic" or "Intimate" if that creature is romantically involved with, or otherwise in love with, the player; likewise, a "Hated" or "Nemesis" condition might exist if the target has a real, deep-seated enmity towards the player.

Risk-Reward Analysis
The more favorable a deal is to the target, the more likely he'll be to accede. Contrariwise, a deal that's likely to result in the target's death is extremely likely to be rejected. The DM should assign a floating modifier, -10 to +10, to the check DC, with a favorable deal resulting in a negative modifier and an unfavorable deal resulting in a positive modifier.

Examples:
 * A bard offers a group of guards 20 platinum to look the other way while he and his friends sneak into the Governor's ball. As 5 platinum apiece is equivalent to a few months' pay for a guard, and the worst-case scenario is that the guard gets fired, this is a favorable deal and worth a -5 to the DC.
 * A blackguard offers his defeated prisoner a choice between slavery or death. While slavery is unpleasant, it's worse than dying, so this is a slightly favorable deal and worth a -2.
 * A corrupt noble offers an assassin 1000 gold to poison the king's food. While the danger to the assassin is slight, the consequence of being caught is execution for treason. The 1000g is a low price to deal with that risk, so this is an unfavorable deal and worth a +3.
 * A stranger tries to convince the captain of the guard to let him borrow the key to the guardhouse for a couple days, offering no bribe or other compensation. As the captain has nothing to gain and everything to lose, this is an unfavorable deal and worth a +10.
 * An average-looking man attempts to seduce a bored elf woman at the bar. While she's not feeling particularly attracted to the man, she is very bored and the night would go by faster, making this an even proposition worth a +0.

Synergy Bonus
5 ranks or more in Bluff grants a +2 synergy bonus to Negotiation. 5 ranks or more in Sense Motive grants a +2 synergy bonus to Negotiation.

Try Again
If a player's initial offer is rejected (i.e. the check fails), but it fails by 5 or less, the target will respond with a counter-offer, usually one that ups the risk-reward ratio to favorable for the target. The player may accept the counter-offer without rolling, or may try a different approach.

If the failure is between 5 and 10, the target refuses without making a counter-offer. The player may try again by sweetening the deal, but each additional attempt beyond the first imposes a -5 penalty.

If the failure is by more than 10, the target will not negotiate further with the player, and his attitude is adjusted down by one step.

Taking 10 and 20
A player may take 10 on a Negotiation check only if the target is Friendly or better. He may not take 20 on a Negotiation check.

In the Field
Argent the bard is 5th level with a Charisma of 16. He has maximum ranks in Negotiation (8) and the synergy bonus from Bluff, so his Negotiation check is +13.

Argent wants to get into the Governor's Ball, which is being held at the castle of Tanjar the Dread. Argent approaches the four gate guards and slips one of them 50 gold to let him into the party.

The guards are level 3 warriors, so Argent's base check DC is 18. The guards are treated as Unfriendly, since they have orders to keep out anyone not on the guest list. This increases the DC to 23. Argent assumes that the 50 gold bribe will be enough to at least get their attention; after all, that's almost half a year's pay for a guard. Argent's player is attempting to get at least a Neutral risk/reward analysis.

Unfortunately, Argent has failed to consider that, while 50 gold is a lot for one guard, there are four guards there. Likewise, Tanjar the Dread didn't come by his moniker for having particuarly natty hair, and is known to punish and even execute servants who fail in their duty. Thus, the reward isn't very good, and the risk is very high. Argent's deal is unfavorable to the guards, worth roughly a +8. This makes the final DC 30, meaning Argent needs a 17 or higher on the die to succeed.

Thinking fast, Argent charms one of the guards, changing his demeanor to Friendly. Argent's DC for that guard is now only 20. Unfortunately, the three other guards are still at 30. Argent tries the roll anyway ... and rolls a 15! Failure.

However, he has only failed by two. The charmed guard immediately nods and waves him in, but the other guards stand in his way, demanding their 50g each ... with an extra 50 on top for his impoliteness at not offering them a cut in the first place. 100g each would be enough to get away from Tanjar if things go sour, making the deal slightly favorable for the remaining guards. Grumbling, Argent ponies up the extra 300g, and the guards step aside.

Later that night, Argent is attempting to seduce the Governor's daughter. He is attractive and charming, so that's in his favor; if her father found out, though, she would be severely punished. However, being seen to consort with such a well-known rogueish character would bolster her social reputation. Her attitude is Indifferent and her risk/reward analysis is slightly favorable; her five levels of Aristocrat make the base DC 20 with a -2 modifier. Argent only has to roll a 5 or better to sweep the Governor's daughter off her feet.

Analysis
A character who is working on being a skilled negotiator has level + 3 ranks in the skill, and the DC is 15 + the target's hit dice. Given equal attribute modifiers (CHA vs WIS) and equal hit dice, the check is +3 versus a DC of 15, giving success on 12 or higher for an even proposition to an indifferent party. This is nice because most people are mildly disinclined to do something that they have no stake in for someone they're indifferent to. A friend (-5 DC, DC 10) is much more inclined (7 or higher on the die) and a good friend (-10 DC, DC 5) is even more inclined. A lover (-15 DC) is guaranteed to do something for his love even if there's no direct benefit.

A modest quid pro quo evens things up considerably, making friends very likely to help (I'll buy pizza if you help me move) and guaranteeing that a best friend will help. A tit-for-tat even helps indifferent people lean towards helping rather than not.

But what about people who are untrained in negotiating? Well, the skill can be used untrained, but people who are both important and savvy (like most higher-level characters) are generally disinclined to be helpful unless there's something in it for them. So while an "average joe" first-level character trying to talk an average-joe friend into helping him move (+0 check vs. DC 16 - 5 (friend) - 5 (pizza) = 6) has a pretty good chance of succeeding, that same average joe would have a much harder time convincing a relative stranger, particularly if that stranger happened to have better things to do (DC 18 for a level 3 stranger, +0 indifference, -5 pizza = DC 13). Still not insurmountable, but it demonstrates that people who haven't taken pains to be good at negotiating are going to have to "sweeten the deal" a lot more to get their own way than someone who's practiced at making friends and influencing people.