The combination of the four C’s is what ultimately determines the price of a diamond. And the best confirmation of the quality of the diamond is an independent international laboratory certification. However care must be taken to the certifier used for the chosen diamond as all have a different set of standards to grade against. GIA and HRD are the most common and highest regarded certifiers with IGI and DCLA in the mid range and EGL and AusCert being very lenient in their standards.
The better regarded the certifier the more it can potentially be worth in the market. As it is often the cutting factory that sends the diamond out for certification they will know the general quality of the diamond and send it where that particular diamond will receive the highest rated grading. Their best diamonds will go the the strictest and best certifiers and any poorer quality stones will be sent where they will get the most leniency. This will achieve the best grade possible and result in the most money for each diamond. To get a true indication of the quality of the diamond we suggest only buying a diamond certified by either GIA or HRD who are highly as the premier certifiers.