I'm liking this manga so far. The protag is not over powered but is able to live interestingly simply because of their ability to see things from another perspective. Also the reasoning they have going is fairly good as well.
I have seen many comments criticizing the usage of salt, but it is perfectly reasonable. In the world the author has created the dietary need for salt is gone (magic muggufin), thus it has turned into a spice only. With it's rarity it can be compared to saffron. Saffron is not rare, and is not hard to cultivate, but it's current market price is about 2,000$ per kilo. It is a luxury spice, and not used in many common dishes.
Now the protag wants it because they are used to having it in their diet, and for the taste. So they use modern economics to make it available. First they up the demand. With demand, the supply will increase, but if it goes the way the protag is hoping, the demand will outstrip the current supply, making more traders bring it in. Which will start a battle to for the traders to sell off their salt, which is won by traders lowering their price, just a little below what others are selling at. Eventually the price will level off, but be substantially lower than the luxury price it was initially. (this happened with chocolate) And the reason the initial seller is going along with this, and even giving them salt for free to create the want, is that the first sellers (before the other traders bring in more) will stand to gain a huge profit.
Well done to the author.