If I was even remotely able to afford a piece like that I would have an appraiser looking at it immediately as most people that can afford pissing off 8 mil do. If he got took, it's his fault.

Jewelers are appraisers. At least all good ones are. Anytime you buy a piece of fine jewelry made by a jeweler they almost always include an appraisal, which is also required for insurance purposes. It sounds to me like this jeweler misrepresented the value on his initial appraisal. That could be grounds for winning a lawsuit.