CAC (Certified Acceptance Corporation) is the only 3rd party authentication service that looks for "solid for the grade" coins. These coins typically bring 15-35% more than "average" quality coins.
CAC also designates "exceedes quality standards for the grade. These coins receive a gold sticker, and typically trade at price levels of one grade higher than the actual grade on the coin. Sometimes prices exceed that of the next price level as well.