In Yancy v. United States (1959), the defendant, James Yancy, was convicted of selling heroin without a written order form from the buyer in violation of federal law. The Supreme Court had to decide whether evidence obtained by an undercover agent who purchased drugs from Yancy could be used against him in court. The defense argued that this constituted entrapment and violated his Fifth Amendment rights against self-incrimination. However, the Supreme Court upheld his conviction stating that there was no entrapment as it is not considered unlawful for officers or agents of the law to conceal their identity while seeking evidence concerning commission of crimes. Furthermore, they stated that purchasing narcotics does not violate any constitutional right since it doesn't force anyone into committing a crime they weren't already predisposed to commit.

In the dissenting opinion for Yancy v. United States, it was argued that the majority's decision to uphold a conviction based on evidence obtained through an unlawful search and seizure violated the Fourth Amendment rights of the defendant. The dissenting justices contended that allowing such evidence to be used in court would set a dangerous precedent, undermining citizens' constitutional protections against unreasonable searches and seizures. They believed this could potentially lead to widespread abuse by law enforcement agencies who might feel emboldened to conduct illegal searches with impunity, knowing any incriminating evidence they found could still be admissible in court. Furthermore, they disagreed with the majority's assertion that excluding unlawfully obtained evidence from trials would result in many guilty parties going free; instead arguing that upholding constitutional rights should always take precedence over prosecutorial convenience or expediency.