What Is A Certified Coin?
First, a coin is purchased in its "raw" state by a trained numismatist. At this stage the risk of financial loss is greatest.
Next, the coin is sent to the Numismatic Guaranty Corporation, an independent non-biased entity, which "certifies" its grade and authenticity for the entire market.
Finally, the graded coin is sonically sealed in a hard plastic tamper-proof holder. This eliminates potential bias with respect to a coin's grade. At this stage a novice can attach a value without the aid of a trained numismatist.
Most experts agree, this is the most secure way to purchase rare coins!