Certification. A written report from an independent gemological lab grading a diamond against the 4 Cs and other characteristics. On the resale market, GIA reports are the gold standard; AGSL is comparable. EGL and IGI reports exist but are typically re-graded by professional buyers.
A grading report is not an appraisal. It states what the diamond is — it does not state what the diamond is worth.
If your stone is over half a carat and has no report, ordering a GIA report (typically $48–$113) usually pays for itself in a higher final offer.
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