The New York Times has more details on the busts: Four California Museums Are Raided.

At the center of the investigation are the owners of the Silk Roads Gallery, Jonathan Markell and his wife, Cari Markell, and Robert Olson, who is said in the search warrants to have smuggled looted antiquities out of Thailand, Myanmar and China.[…]

In more than 120 pages of search warrants and affidavits, the authorities described one typical transaction as follows:

The Markells would acquire an object from Mr. Olson and then offer it for sale to the undercover agent for about $1,500. They would provide an appraisal valuing the object at close to $4,990, an amount calculated to get around tax regulations requiring more documentation for bigger donations. The appraisals sometimes falsely stated that the estimated values were prepared at the Southeast Asian Museum in Bangkok. The Markells would then arrange for the donation of an object to a museum.

This is a typical scam. The dealer sells his stolen wares to collectors who then donate them to a museum. The dealer makes bank, the collector gets a fat tax break, and the museum gets goods they can hastily provenance as “donated from the private collection of Mr. and Mrs. Smythe, Esq”.

In this case, there was a nice tax fraud element too — when will people learn the lessons of Al Capone? — but even without the inflated estimates, this process often serves to obscure theft. It’s an antiquities laundering operation, basically, and everyone in the ring benefits.