The 5th C - Diamond Certificate
It is a natural but unfortunate temptation for a diamond seller to overstate the quality of the diamond he is selling. A certificate from an independent, well respected laboratory (providing it is the one that matches the diamond) is your guarantee of quality. Among the most respected laboratories are the GIA, HRD, IGI, AGS, CIBJO & Anchor Certificates. Beware of obscure laboratories whose certificates are rarely worth the paper they are written on.