“The art market has changed,” Coulson says. “It has gone from professionals only to a kind of luxury retailing where you have no idea who you are dealing with.”

At the high end, enthusiasm about China's allegedly endless appetite for luxury brands is pushing up stocks like LVMH, which now trades at about 3.5x book value on the hope of rapid growth.

There are gangs and a thriving black market for smuggled luxuries, a current inmate says, such as liquor, shrimp, chicken and cigarettes, which can fetch $10 apiece.