Almost all the diamonds look alike but their quality might not be the same. The quality of a diamond is the most important thing to check while purchasing a diamond. A certified diamond gives the guarantee that the diamond is of high quality, and without it, you have no assurance that the diamond you are purchasing is of the quality you're paying for. Thus, certification is important as it is used to examine a diamond’s value.
It is not necessary that you must buy a certified diamond, you can also buy an uncertified diamond, but on your own risk. The quality of an uncertified diamond is not guaranteed. It might be having a great quality or might not. Both certified and uncertified diamonds are similar, only the difference is the piece of paper i.e. what we call a diamond certificate or a diamond report which is provided with a certified diamond but not with an uncertified diamond. There is not always difference in the price of a certified and uncertified diamond, but sometimes a certified diamond is sold with a higher price than an uncertified one, because the certificate helps the consumer to confirm the quality of a diamond they are paying for.
Thus, to get the best quality of a diamond, a certified diamond is recommended and this certification is obtained from the trusted gemological laboratory based on the four important properties color, carat weight, cut and clarity. And the most common labs for testing the quality of a diamond are Gemological Institute of America (GIA), European Gemological Laboratory (EGL), International Gemological Laboratory(IGL), International Gemological Institute(IGI), Hoge Raad Voor Diamant(HRD), American Gem Society (AGS).
So care must be taken while purchasing a diamond so that you may get the best.