Haggling is an easy to way to reduce the cost of any purchasable item from vendors. It is a good idea to haggle for any expensive items such as weapons and armour; you will always get a reduction. It is possible to haggle successfully for any item that you purchase, but you should also consider your reputation with vendors and settlements. If you haggle unreasonably too often, your reputation with that specific vendor and the settlement they are associated with will diminish. In addition, all items purchasable from that specific vendor will increase in price. This works both ways; if you decide to pay more for an item, your reputation will increase with the vendor and the associated settlement, and the cost of items in general will be reduced the next time you visit them. It is also worth noting that being too persistent with a stated amount will cause the vendor to become angry. You will have two to three chances to haggle for a specific amount before the vendor abandons the deal.
Note: It is recommended that you haggle for items to be reduced between 10 - 20% at the beginning of the game. This will ensure that you do not excessively diminish vendor and settlement reputation, while still saving money. As you acquire more Groschen throughout the game, you can revisit vendors and settlements to return the favour by paying more than an item is worth, thereby improving reputation when you can afford it.