A handyman who does work for me prefers for me to pay him in cash. Am I committing a sin if I agree to do so? It is fascinating to see how virtually the whole country has become engaged in the intricacies of moral debate on this issue, including the complex question of material or formal co-operation in evil. The broad consensus is correct according to Catholic moral teaching: there is absolutely nothing wrong in itself with paying somebody using cash, which is, after all, legal tender. However if we pay cash because of an explicit offer to reduce the cost of the work, and because this reduction is due to the evasion of income tax or VAT, then we are formally co-operating in evil, and committing a sin (probably a venial sin given the amount of tax normally involved.) If we simply have a suspicion that cash is requested in order to avoid tax, then we ought (within reason) to ask whether this is the case or not. The costs that small businesses incur with bank charges, credit card me...