The grade of a coin can go from 1 - 70, denoting condition. Grading coins is an art form that takes years to master. Professional grading helps to assurre the value of the coin. A coin in top pristine condition can be worth 1,000 times or more than a coin in less valued condition. You also have to be concerned about fakes and fraudulent coins, as much money could be lost.
This was a neat, succinct link to an explaination on grades of coins, and the professional companies that grade the coins.
http://www.nostomania.com/servlets/c...insGradingMain