Every diamond over .50 carats comes with a certificate from a lab. However there are wide ranges of quality within each grade of diamond. There is more to know about a diamond than what's written on paper.
Every diamond is completely unique even within the four C's- Cut, Colour, Clarity and Carat. Flawless and colourless VS+ diamonds only make up a small percentage of diamonds sold. Gary has personally purchased diamonds with lesser grades that are still beautiful and represent better value.