 Private assay offices catered to the individual prospector, and to miners who stole gold out of the mines.Mine owners were concerned about ore theft, and several large mines hired Pinkerton agents beginning in 1897,p.75 but high grading — the theft of rich gold ore by miners — was difficult to control.Jameson observes that "the Mine Owners' Association paid (someone) to blow up assay offices in 1902 to try to stop high grading."