If you have chosen to buy a diamond for someone, you’re probably already asking yourself one of the most important questions: where will I buy it and who will give me the best price? Can I trust my jeweler to guide me in the right direction/to give me the best advice, or should I pursue another solution that will better meet my needs?
If you opt for the latter route, here are some guidelines to help you get started.
The most important step is to understand how diamond quality impacts its price. When it comes to determining quality, there are four essential elements, known as the four Cs: Clarity, Color, Cut and Carat. Without dwelling on technical details for the moment (we’ll get to that in a future post), with a fixed budget, your choice will fall somewhere between a larger diamond of lower quality and a smaller, but higher quality diamond.
It’s widely held that the preference for clarity (grade I.F.) and white (color rating D, E or F) diamonds often undervalues the importance of cuts that can impact a stone’s brilliance.
My vision is the opposite: Why choose a diamond that has an imperceptible difference in tonality (i.e. less white) or a small inclusion, even if it’s only visible under a microscope, that is also less brilliant?
It should also be noted that while the visible difference of a single grade of color or clarity may be invisible to the naked eye (even by a skilled gemologist), the difference in price could be remarkable, especially for diamonds of higher carat weight. Similarly, the difference between a discreet cut and one that is excellent is also not always obvious. 
Once you’ve identified the suitable quality, you will want to request credentials that can authenticate your stone’s described quality. The only internationally recognized commercial certification organizations in the world are: the GIA, HRD and the IGI (a fourth would be the AGS, although this is less used in Europe because their assessments are thought to be extremely severe).
I would caution against other agencies—some for reasons of trust, others because they are not known on the international level. It’s worth pointing out that in recent years, we have heard complaints about the evaluation parameters of some gemology laboratories, who, when called into question, offered the defense that gemology is a subjective science. This is another topic worth discussing that we will get into at another time.
Having selected the diamond that bests suits your needs (let’s make the example of a stone of 0.70 carats, clarity of VS2, color G, cut Excellent, and GIA certified), the next step is to figure out where you can buy it at the best price. With the knowledge gained by a clear understanding of the elements described above, you should be able to avoid any sellers who would take advantage of an inexperienced buyer.
I’ll share one last tip. Buying a diamond is no small purchase; in addition to the obvious financial investment, it also has great symbolic value. No matter which jeweler, financial institution or online agency you choose, you will want to make sure that any company that you plan to do business with has a solid reputation for being serious and honest.