That could be the title of a long book. Short answer you cant ." The" or a certificate is only part of the puzzle of the value of a stone . Let us stay with ( the certificate ) certificates come in 3 rough types fraudulent , meaningless and help full Ok let us say you have a help full one and this stone is not very large or rare you can look up the price in a wholesale catalog . And yes you may have something nice. If it is large or rare get a second opinion . best of luck and skill to you .