Is a diamond certificate indispensable?

Short answer, yes, definitely!  Whenever you are shopping for diamonds, the very first thing you should ask your wholesaler is whether the diamond comes with a certificate.
Ideally, a renowned institute like Gemological Institute of America (GIA) or American Gem Society (AGS) should issue the grading certificate. Another known grading institute is the European Gemological Laboratory (EGL).  GIA and AGS are stricter when they grade the diamond, whereas EGL is more relaxed. A highly recognized certificate is also beneficial if you plan to sell your diamond in the future.
Do not accept a diamond that comes with an in house document or grading from a supposedly 3rd party neutral grading company. Be very alert and skeptical at this point. These are simple marketing tactics that unethical jewelers employ to make it seem like their diamond comes from a reputable grading company.
Purchasing a diamond is a very important decision. You spend money investing in your precious stone. You want to make sure it is graded from a reputable institute so it is validated that you are purchasing a registered diamond.
A diamond certificate accompanies every diamond sold at Diamond Deals. A diamond certificate assures that a reputable institute has graded your diamond. Further, your diamond has been registered.