I've never been able to get a firm answer on what exactly tariffs do.
Some people say things like "raising tariffs on foreign goods makes it easier for your national factories/artisans to compete on the domestic market." This certainly makes sense in the real world, but then you have people say "pops always buy from the internal market first."
Likewise I don't know whether or not, in game terms, tariffs affect the cost of domestically produced goods.
Take steel for example. Lets say your domestic producers make 10 steel and your country demands 15 steel. Let's further assume the cost of steel is usually 10 pounds, but you use tariffs to raise it to 15. Does this mean:
1. All steel in your country is purchased at 15 pounds. The government pockets the extra 5.
2. All steel in your country is purchased at 15 pounds. The government pockets the extra 5 on foreign steel (this is what I assume happens.)
3. All foreign steel in your country is sold at 15 pounds and the government pockets the extra 5. Domestic steel sells for 10.
If it's 1 raising tariffs should have a net negative effect on your artisans/factories. They get no extra money from their sales but they have to pay more for inputs and needs.
If it's 2 well then things make sense more or less, but raising tariffs increases the price of steel as an input to other factories, even for the 10 steel you are not importing. (This makes sense from a real world standpoint, but might be counter intuitive to some players.)
If it's 3 then again raising tariffs should have a net negative impact for the same reason as it did for 1.
I assume that 2 is what happens and that the effect of tariffs on the price of a good is decided by how much of that good is imported vs. produced domestically. So if your country is a net exporter of fruit then no matter what you do to tariffs the price of fruit will not change, but I don't know that for a fact.