The unspoken 5thCs is the confidence in the person in front of you and in the gemological certificate that verifying your purchase.

Anyone who stands in front of you, whether you are working with, buying from or selling to, he must instill a feeling of trust, honesty and reliability. Not all certificates are accurate and truthful information, especially not all of them are internationally recognized.
A certificate with excellent reputation and international recognition is highly recommended in every purchase.

Today if someone is trying to sell a diamond/jewel for much less price than anyone else, there usually is a reason for why it is so much less.

MASSIMO RAITERI recommends exclusively purchases in a reputable jeweler that you trust and to full inform before on the gemological certificate and warranty issued.