In theory, the shipping containers that travel the oceans are not limited by weight, but rather by cubic feet. A standard 44 foot container will hold about 2,500 cubic feet of material.
But after leaving the ship, they have to travel by truck or train. If by train, again the weight is not a concern. But if by truck, the maximum weight will either be 40,000 pounds or 44,000 pounds.
So, if you are shipping heavy items like solid brass bar stock, the container might be only 1/4 full by cubic feet.
You could fill the container with 35,000 pounds of brass and the 5,000 to 9,000 additional poundage be made up of fire wood. Essentially, the fire wood would travel for nearly no cost.
So there are ways around these things.
Plus, some countries have quirky tax rules. And those can make money-losers really be money-makers. And unless you know the laws of that country you will never figure out how they priced things out.