First, get the Final Offer perk. To find this perk, navigate to the "Player" section of the menu. Go to "Stats" and find "Speech". Expand it to see the Speech perks. You need Speech Level 4 to choose the Final Offer perk. Its description reads: "When a trader loses patience with you during haggling, you have one more chance to make another offer." While this may not sound too great, it actually is very helpful. Once you have bought or sold your items, check your basket. You can see a Haggle button in the lower left corner. Hold the button to bargain on the price. Once you know how to haggle, simply use the Final Offer perk to maximize the benefit every time. When you are haggling with a merchant or someone else, immediately drop to the lowest (when buying) or highest (when selling) price available. The perk will automatically kick in and let you have another chance, but the merchant will now be offering the best possible price. This allows you to get discounts of 50% and better.