Valuation of diamond out by 0.3 carats

Marius Nel issued a valuation certificate on a diamond ring. The owner wanted to sell the ring. The seller met us at his shop. He confirmed the valuation and suggested that it is a very good buy and we trusted his professional opinion. The valuation of the diamond was on a 0.8 carat diamond. The ring was in a setting and he assured us that the worse case the diamond would be 0.7 carats. When the diamond was removed from the settin, measured and weighed, it was 0.49 carats which made a huge difference in the value. Marius Nel caused us to lose a lot of money with this inacurate valuation and estimate.