Not buying certified diamonds is like buying a car without a title.

A diamond certificate is an expert third party opinion. It states the quality of the certified diamonds. Without the certificate you are left to trust the jeweler's estimates. This can cause a potential conflict because the jeweler is the one trying to sell you the diamond.

Buying a certified diamond usually cost a little more because the diamond had to go through a lab of gemologists that graded every aspect of the diamond.

There has been much talk on the internet as to which certificate is the best. They all have slightly different grading criteria. The important thing to keep in mind is if you send one diamond to three different labs you might get three different grades but they will most likely only be different by one grade at most.

These labs are paid to get the most accurate grades possible but some of the things that they grade have a bit of subjectiveness to them. Meaning the decision will have to be made by a human. A machine can't just generate a grade.

This applies to clarity. What is the difference between a VVS1 and a VVS2. To you and me not much. In fact given a microscope and a diamond we would be hard pressed to see the difference.

The three main labs that you will run across on the internet are

These are three very reputable labs. Other labs exist that grade diamonds but most will be from one of these three labs.

If the diamond that you are looking at has a certificate from a different lab I would highly advise that you do some research about the certifying lab.

These stores sell certified diamonds.