This is a definition problem I think. I don’t use the word “responsible” to mean sole ownership. For example. We are all responsible for the cleanliness of our roads. It is a shared responsibility that we all participate in.
And, I think, we are all responsible for modeling good behaviors for people to emulate.
If the person in the US is only willing to pay 70, then the artist will get less than 70.
Sure, the American pays the tariff. That’s not the point. The point is that this person wants to spend X total and wants most of that X to end up with the artist. And that doesn’t happen if they have to spend half of X to pay for the tariff.
The point of saying “the American pays the tariff” isn’t to say that the seller makes the same amount. It’s to emphasize that the seller won’t absorb that cost, which is the lie Trump is selling.