Haggle

Haggle (Cha)
If you dream of riches, haggle will be your best friend, allowing you to buy and sell for much better prices.

The basic formulas are: Selling = Base SELL percentage + (0.25% * Haggle). (With a maximum of 50% after Haggle is applied.)

Base SELL percentage is:
 * 10.00% for most Vendors.
 * 12.50% for Vendors after you have completed a specific Reputation Quest for their area (see table below).
 * 15.00% for all Pawn Brokers (except Vahna Smythe at the Pawn & Gift Shop in the Spa in Ataraxia, which is always 12.50% base).
 * 7.50% for Azdaf the Wary - Yugoloth Alchemist in Amrath and Marraenoloth - Yugoloth Ferryman in The Shroud (making it extra wasteful to sell loot to them: don't sell stuff to Azdaf at all, and if you need to sell to Marraenoloth you can buy it back for the same price after you get outside of The Shroud and re-sell it to Pawn Brokers or normal Vendors).

Buying = [1 - (0.005 * Haggle)] * Markup percentage. (Markup percentage varies depending on Vendor/level of Broker, with a minimum of 50% after Haggle is applied.)

This formula can be rewritten as:

Buying = Markup percentage - (Markup percentage * 0.005 * Haggle) = Base BUY percentage - (Per Haggle Modifier * Haggle)

So, the lower the Markup (AKA Base BUY percentage), the lower the Per Haggle Modifier too (so you get a better rate over-all, but slightly less per additional Haggle skill level).

BUY Markup is:
 * 120% for Vendors before the associated Reputation Quest has been completed (if available).
 * 120% Base BUY percentage, -0.60% per Haggle
 * 117.5% for Vendors after the associated Reputation Quest has been completed.
 * 117.5% Base BUY percentage, -0.5875% per Haggle
 * 110% for non-Guild Hireling Vendors (making Hireling Contracts slightly cheaper than their base price alone would normally imply, and even cheaper when purchased from the Guild Hireling Vendors).
 * 110% Base BUY percentage, -0.55% per Haggle
 * 100% for all the Guild Vendors in House Kundarak and also the Airship Vendor accessible via any Hook Point on a Guild Airship. So, items purchased from these stores are unusually cheap.
 * 100% Base BUY percentage, -0.50% per Haggle
 * 125% for ml:2/0 Brokers
 * 125% Base BUY percentage, -0.625% per Haggle
 * 127.5% for ml:4/5 Brokers
 * 127.5% Base BUY percentage, -0.6375% per Haggle
 * 130% for ml:6/7 Brokers
 * 130% Base BUY percentage, -0.65% per Haggle
 * 135% for ml:8/9+ Brokers
 * 135% Base BUY percentage, -0.675% per Haggle
 * 240% for Azdaf the Wary - Yugoloth Alchemist in Amrath and Marraenoloth - Yugoloth Ferryman in The Shroud (making it extra expensive to buy Yugoloth Mercenary Potions and Shroud supplies, respectively).
 * 240% Base BUY percentage, -1.20% per Haggle
 * 400% for Haddad the summoned Efreeti Forgemaster (from the Repair Anvil DDO Store item). Luckily there isn't much to even want to buy from him.
 * 400% Base BUY percentage, -2.00% per Haggle

Haggle is a Class Skill for Artificer, Bard, Rogue See (forum post) for a good Haggle Bard build.

Maximum Theoretical Haggle (118) as of U13
Completionist Drow : 19 Rog / 1 Brd

Charisma 54 (+22)
+20 Base +5 Levelup +4 Tome +2 Completionist +7 Enhancement (+7 item) +3 Exceptional (ToD Ring) +2 Artifact (+2 Airship Charisma Shrine) +3 Alchemical (Potion of Influence +3) +2 Untyped (Essence of Seduction) +2 Untyped (Lasting Eagle's Majesty Potion) +4 Profane (Abishai Destroyer)

Items (+27)
+15 Competence Item +6 Exceptional (Green Steel Charisma skill item) +2 Luck (Good Luck +2) +4 Guild (Large Gem of Haggling)

Character (+45)
+23 Ranks +5 Rogue Skill Boost IV +4 Improved Haggle IV +4 Skill Mastery x4 +3 Skill Focus : Haggle +2 Completionist +2 Negotiator +1 Past Life: Bardic Dilettante +1 Past Life: Sneak of Shadows

Buffs (+24)
+5 Enhancement (Dwarven Stoutness) +5 Insight (Moment of Clarity) +4 Morale (Greater Heroism) +3 Alchemical (Potion of Eagle's Skill +3) +2 Untyped (Walk of the Sun) +2 Untyped (Inspire competence) +1 Circumstance (Focusing Chant) +1 Profane (Elite Spider Cult Mask) +1 Psionic (DeGenevev Succubi Marketplace Event)

Progression table
Vendors and Tavernkeeps buy and sell at rates based on completion of a specific Reputation Quest. Talk to the City Ward greeter or contact for specific information on Reputation quest (or see full list below). Brokers have varying rates based on minimum level of items in which they deal (eg., ml:2/0 Broker refers to min level 2 weapons/armor brokers and min level 0 clothing/jewelry brokers).

Update 7 stealth-nerfed the Guild General Vendor in House Kundarak again, he now only pays 10.0% base. Do not sell to him. Dev Tolero implied this was an error that will be corrected in the future (link).

Here is how Haggle impacts the buying and selling price of items, at the different vendors.

Example: A player character with 0 Haggle skill wishes to buy a ml:2 weapon from the Broker. The base value of the weapon is 8,000gp. The ml:2 Broker markup is +25%. So the player can BUY for 125% ItemBaseValue, for 10,000gp. The same player uses another character with 40 Haggle and can BUY the item for 100% base value, for 8,000gp.
 * Per Update 14 Release Notes, "Vendor buy/sell prices are now limited to 50% of the item's base price." (Needs in-game verification.)

Reputation Quests
1 Does not include the Guild Vendor or the vendors in the Crafting Hall, who use Vendor base