In Trist v. Child, the Supreme Court invalidates contingency contracts for lobbyists. In the opinion, the Court states:
To legalize the traffic of such service, would open a door at which fraud and falsehood would not fail to enter and make themselves felt at every accessible point. It would invite their presence and offer them a premium. If the tempted agent be corrupt himself, and disposed to corrupt others, the transition requires but a single step. He has the means in his hands, with every facility and a strong incentive to use them. The widespread suspicion which prevails, and charges openly made and hardly denied, lead to the conclusion that such events are not of rare occurrence. Where the avarice of the agent is inflamed by the hope of a reward contingent upon success, and to be graduated by a percentage upon the amount appropriated, the danger of tampering in its worst form is greatly increased.