In the U.S.–Mexico borderlands during the late nineteenth century, concern about the existence of mining fraud—be it stock manipulation, salting, or straight-up false advertising—was prevalent in the mining community. The belief that fraud was endemic in the region forced the small community of mining engineers working there to tailor their presentation of themselves as technical professionals in relation to these pervasive concerns about fraud. The ways in which mining engineers in this time and place addressed the problem of fraud illustrates how technical-knowledge claims are mediated through the local concerns of professional engineers.