While the World of Diamonds has always been assosicated with Glitz and Glamour, as people become increasingly knowleadgeble about Diamonds both the layman and the expert, there is value to be found and pitfalls to avoid that will ensure you walk away with the right stone and the right price and from the right source.
Additionally, the layman need not worry about having to undertake any major research into the world of Diamonds in order to make an informed purchase, the laboratories that grade Diamonds, the trade industry bodies and market players are largely geared towards removing industry jargon and standardisation of terminology.
In essence if an expert and a layman were to come together and asked to choose between or rank 5 or 10 diamonds based on their certificates or quality parameters, it is highly likely both would come to the same or similar ranking. This is very different from 30 years ago where certificates were considered unnecessary or an additional cost or the reason diamond prices get inflated.
All in all, if the Diamond looks good and does what you expect a Diamond to do, which is sparkle, have luster, have presence then it is likely a good diamond and in order to make sure, you have supplementary materials at hand e.g. certificates from bonafide laboratories, independent appraisals from accredited bodies or expert advise. Finally, however the decision should be a culmination of the above and superseded by your instinct.