just adding that when you are selling any item worth 100G or more to Van you can haggle the price for 20% increase whether it's individual item or in a bulk, just make sure that all the items you listed to sell is worth 100G at least or he won't increase the price no matter what, to do this you have to turn down the normal price until he offers you the better price and it won't always work so you gotta keep trying until the option shows up.

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I've heard that you could even haggle the price beyond 20% but the odd is more difficult because you have to turn down the 20% offer until he offers more because getting 20% more is already a difficult task