A person or the agent of any person engaged in milling, smelting, sampling, concentrating, reducing, shipping or purchasing ores in this state, who in any manner knowingly alters or changes the true value of ores delivered to him to deprive the seller of the correct value thereof, or who substitutes other ores for those delivered, or who issues a bill of sale or certificate of purchase which does not exactly and truthfully state the actual weight, assay value and total amount paid for any lot of ore purchased, or who by secret understanding, or agreement with another, issues a bill of sale or certificate of purchase which does not correctly and truthfully set forth the weight, assay value and total amount paid for the ore purchased by him, is guilty of a class 6 felony.