Items whose live Grand Exchange price has dropped at least 3% against its own 24-hour volume-weighted average — the dip-buy candidates worth a second look, not a static "worst performers" list.
A raw price drop can just be one seller dumping a single stack. This list only counts items trading 100,000+ gp mid-price and 100,000+ daily volume, so a real move on Coal or Adamantite bar means broad selling pressure, not one whale — the kind of dip a flipper can actually act on.