Diamond rough valuation varies with each cutter's resulting polish value [causal]
The value of a rough diamond depends on the value of the polished stones that can be manufactured from it. Since no two diamantaires will cut a stone the same way, the value added in the manufacturing process varies widely. Consequently, when dealers value a piece of rough differently, that difference, on which profitability turns, often reflects a real difference in the value of the polished stones they will be able to cut from it.
DEFINE: Explains why buyers of rough diamonds can legitimately value the same stone differently: value is contingent on the manufacturing outcome, which varies by cutter.
Lisa Bernestein, Opting out of the Legal Sys…, loc. 26