I don’t consider the purchase of a diamond to be an e-commerce item and I don’t recommend anyone just selecting a diamond and putting it into a shopping cart for purchase.
A certificate and statistics are only a clinical description of a diamond, and they do not necessarily reflect the beauty or desirability of a diamond. For example, two diamonds may have the same certificate grade of, let’s say, F color and SI2 clarity. However, they can, and often do, differ in the “quality” of their grades. One may be a strong F color — close to an E color — and the SI2 clarity grade close to an SI1, while the other can be much weaker in both categories. In fact, the nature of a diamond’s actual clarity, as opposed to its clarity “grade” may make a lower graded diamond more desirable than a higher graded diamond and save you money. This may be true even if both diamonds are graded by the same gemological laboratory (for example, both GIA) and especially true with diamonds graded by different laboratories (for example, GIA vs. EGL). Although cut measurements may also be similar, the intrinsic brilliance and beauty can, and often do, differ since each diamond has its own individual identity and character. The value and investment desirability will therefore vary.
The idea that a diamond is a “commodity” and that all you have to do is find the best grade at the lowest price to assure yourself of a great deal, is a recipe for the purchase of an undesirable diamond. In addition, the current wave of “branded” diamonds is nothing more than an advertising attempt to sell a diamond at a higher price. What counts is what the diamond really is, not what name you give it.