I don't know what Metro was thinking in that specific situation, but I'm aware of 2 exploits. First is kill your painter and paintings get huge increase in values. If goal was to earn money from painting, that would be exploit. Second one is if you have moveobjects on, you can drag painting from easel to inventory even if just started, and move your cursor over it to see the value /average, brilliant or masterpiece and approximate value, than with undo button put it back on easel if you want to finish it, or delete it and your Sim will stop painting immediately in live mode, and be ready for new try.