I just had a thought with the painting skill.
As it is, it's quite easy to make tons of money Painting, I thought of a more realistic way of selling paintings.
Since each town has an art gallery, I propose eliminating the ability to sell a painting off the easle, or in the "buy" items mode, at least for full value.
Instead, have an option to transfer the painting to the art gallery. Then, as sims visit, they have a chance of liking the painting and buying it, much like sims who leave tips for a guitar playing sim.