Yeah that's a garbage feature. The way it works best is having different economic nodes in which a village/town/city produces specific goods based on the buildings it has. These are produced at a speed based on the input goods they can receive from elsewhere as well as local population, with various needs and such. Lots of goods? Low prices. High need for goods? Higher prices. Distribute these all over the lands/space and add many different NPCs travelling between all the nodes doing trade, now you have an economic system based on supply+demand. The player then tries to purchase low and sell high as they travel from place to place while being limited by their carry capacity + being slowed down the larger their party becomes.

Works well. Feels rewarding. This kind of thing can fit in well in a lot of open world games, not just these sandbox M&B style games, but they don't make the effort.