The answer is simple: one of these is being sold online, while the other is sold at a retail shop, where the vendor has to answer to their client.
The truth about GIA (Gemological Institute of America) lab certificates is that they are not as easy to understand as people think: While the stone on the right may have the same cut, color and clarity as the stone on the left, it is clear that other factors have contributed to it becoming “cloudy”, or white/lifeless, rather than scintillating and clear.
On websites like “BlueNile” or “RareCarat”, the GIA certified diamond on the right would be advertised as “the same diamond at a bigger discount”. Within the wholesale diamond industry, however, the GIA diamond on the right is advertised as “rejection” or “bluff” goods.
There is no such thing as “same diamond, different price”. Diamonds are a global commodity and the value is based on the diamonds' own merits, making it quite difficult to effectively buy diamonds online.
Having your diamond certified is a must, though it shouldn’t be the sole factor in your purchase. Though the 4 C’s, proportions/measurements, and other diamond lab report details are very relevant, they don’t entirely capture a diamond’s beauty.
Diamonds and other precious gemstones are individually unique and the only way to truly compare is to go see them in person! Everyone knows that “a diamond is forever”, but the second most important thing to know about diamonds is that you need to “trust your jeweler”.