Two high-profile scandals in high-end violin appraisals and dealing reveal a shadowy world in which little is as it seems. “Authentication is slippery, essential and a near-contact sport among dealers, who regard one another like Yankees and Red Sox and certify the authenticity of their products themselves. And as both of the current dramas demonstrate, pricing tends to the notional, with no instrument quite like any other. Brokers and consultants flourish in the interstices.”