So how do you avoid such a fiasco? Watch for the fish-eye, which becomes gradually more obvious as the pavilion becomes flatter. In this case, the girdle reflection (one part of the fish-eye) would be extremely obvious! Look for the reflection in the Table Reflection Method to estimate pavilion depth, which would very likely be undetectable in this case. Especially check the diamond under long-wave ultraviolet light to make sure strong or medium blue fluorescence is not present. Medium or strong blue will also devalue white diamonds, at least slightly. In the case of “K” and lower grades, fluorescence can potentially raise the value, since when seen from the crown, it generally gives the illusion of a higher color. Always presume the possibility of at least small inclusions or blemishes hidden under bezels or prongs (such as chips and nicks).
If you’re interested in making the buy, make a tentative offer and let the seller know who the responsible party is for remounting the stone, if a price is not agreed upon. (It’s recommended that you, the buyer, take responsibility for remounting unless the mounting style requires expensive labor). Explain why a firm offer cannot be made on a stone that is hidden from accurate grading and valuation.