This is an interesting / confusing discussion. I have friends that are successful artists / painters. They tell me the they get nothing when their paintings are resold on the secondary market. Apparently they can only "write-off" the cost of their materials. One has a "side deal" with a gallery where they pay him a (very) modest amount when one of his paintings is resold. I'm not an expert or an accountant / lawyer, but that's what I've been told.