Shops don't pay for Ingredients

Main mod: No Ingredient Sale.

With this mod shops don't pay for crafting and alchemy ingredients (weightless items) except for jewels (amber, flawless emeralds etc) and monster parts. And pay reduced rates on low value junk (old pelt, razor etc), monster parts and runes/glyphs. The reduced rate is set so that the cheapest of these items only sell for a coin or two.

Alternate mod: Shops don't Pay for Junky Junk

Now included in  LEGO - Loot Economy Gear Overhaul.

By default with this mod shops will pay only pay 1 crown for junk items that aren't tagged as precious(jewelry), valuable(drugs), collectible(fossil) or painting, non-monstrous crafting ingredients that aren't tagged as precious (so you'll still get a high price from things like silver ingots, emeralds etc), non-monstrous alchemy ingredients that aren't tagged as valuabe (so you can still sell monster parts etc), runes& glyphs (their vanilla prices are bloated).

Shops will pay zero for herbs.

Mod menu lets you configure the price multiplier shops buy those junky junk items for (0= shops pay 0 crowns for junky junk items, 0. 01 (default) = shops only pay 1 crown/0. 01% for junky junk, 1 = shops pay 100% full vanilla price for junky junk).

An exception is made for Herbs as they will only sell for 0. This is to prevent the impoverished LEGO player from feeling compelled to pick up every herb/1 coin he sees.

Install:

Same as installing most other TW3 Mods. Avoid Vortex, TW3 Mod Manager recommended  if you need a manager. Place any \modxxx folders directly inside your <TW3 game install>\Mods (or \mods) folder, place any \dlcxxx folders directly inside your <TW3 game install>\dlc (or \DLC) folder. Merge everything with Script Merger.

How to install most simple TW3 Mods for newbies/klutzes:

First you gotta locate your The Witcher 3 game install location. Usually it's somewhere like "C:\GOG Games\The Witcher 3 Wild Hunt GOTY" for Good Old Games versions of the game or "C:\Program Files (x86)\Steam\steamapps\common\The Witcher 3" for Steam versions of the game.

Script Merger

Download, run/install it, run what it installed to be sure it's working.

Optional but highly recommended:

TW3 Mod Manager

Download, run/install it, run what it installed to be sure it's working. Installing it all to some place like C:\TW3Modding\ should work.

Enable the Debug Console: https://www.nexusmods.com/witcher3/mods/3375. Press the keys on your keyboard until you figure out which one activates the console.

After that you can install most mods by downloading them manually (VORTEX NOT RECOMMENDED WITH TW3 MODS, IT WILL EVENTUALLY CAUSE PROBLEMS). Extract their contents somewhere (righ