A diamond certificate is also known as a Diamond Grading Report. This report comes from the Gemological Institute of America (GIA), and you should require this report when you are purchasing a diamond.
With a diamond certificate, you can verify the color, cut, carat, weight, and clarity of the diamond. You dont have to worry about a diamond dealer telling you anything less than the truth, because the certificate comes from the GIA not the dealer. You may be required to pay for the certificate, but the cost is usually low, and in many cases, it will help you negotiate a better price on the diamond or keep you from purchasing a lower quality diamond altogether.
If you buy a high quality diamond, and then later decide to sell the diamond, you will need to have the certificate, or you will have a hard time selling it to someone else. Furthermore, you can use the Diamond Grading Report to look up the wholesale value of the diamond in question. Use the guide that is used by the diamond cutting industry.
With the Certificate, or Diamond Grading Report, there wont be any doubts when you are trying to purchase a diamond. You can easily find out what the diamond is...