The vanilla DFU mercantile algorithm makes it very easy to reach a point where you can sell to merchants their own stuff for more than you bought it for. This mod is intended to make this much harder but by no means impossible by default. You will need to pretty much max out your mercantile and/or use mercantile-boosting gear, and even then you'll be able to swindle only the lowest-quality merchants. The mod can be configured to make this even in easier than in vanilla DFU or completely impossible.

What to expect: selling prices will be slightly less affected by your personality score. The lowest-quality merchants will offer significantly worse deals because their personality and mercantile scores have a higher floor than in vanilla (5 per, 5 mercantile in DFU vanilla, 24 per and 44 mercantile with Tougher Haggling). The highest-quality merchants have up to 100 per and 120 mercantile (this is to simulate them using mercantile-boosting gear, the same way you can). Vanilla DFU ceiling is 100 / 100.

This mod only changes prices when buying from and selling to merchants. It doesn't affect the costs of services provided by NPCs, such as repair, identification, training etc. and should be compatible with all mods that do.

The mod also includes an optional component that allows you to adjust the max loan you can take out. This component is disabled by default for compatibility with other mods that have a similar component.