How do you know the mining company didn’t mix in rough from another source?

Mining companies in the program are subject to very strict regulations in how they operate - from their governments, local and global industry bodies, and other regulators. Non-adherence to these regulations would result in substantial fines and/or a shutdown of their operation. In addition, the mining companies currently in the program are large-scale companies, some publicly traded, and they are audited regularly to ensure adherence with applicable laws and regulations. In addition, GIA has strict guidelines for participants regarding the submission of rough stones for this service.