One of the best tools for art recovery work is the sharp eye of the original theft victim.
Even after a theft, they are still buying, still collecting, and often spot their own item being offered for sale.

Chris Marinello was contacted by the theft victim who was flipping through a Christie’s jewellry catalogue in 2009 and noticed a watch that she lost outside a steakhouse in New Jersey.
Fortunately, she had filed a police report and Marinello was able to stop the sale and recover the item on behalf of the victim’s insurer.

With most fine art insurance policies, victims can simply reimburse their insurance company the original payout amount to effectuate return of their property.