This practice can be harmful to consumers who, if the market power of the firm is used, can be forced to pay monopoly prices for goods that should be selling for only a little more than the cost of production. Nevertheless, it is very hard to prosecute because it may occur without any collusion between the competitors. Courts have held that no violation of the antitrust laws occurs where firms independently raise or lower prices, but that a violation can be shown when "plus factors" occur, such as firms being motivated to collude and taking actions against their own economic self-interests. This procedure of the courts is sometimes called as setting of a conspiracy theory.