472 U.S. 463 (1985).
Undercover officers entered an adult bookstore and purchased obscene materials that led to the arrest of the store’s employee. The undercover purchase was challenged as an unreasonable seizure of the materials. The Supreme Court held that there was no search or seizure at all:
The officer’s action in entering the bookstore and examining the wares that were intentionally exposed to all who frequent the place of business did not infringe a legitmate expectation of privacy and hence did not constitute a search within the meaning of the Fourth Amendment … Nor was the subsequent purchase a seizure within the meaning of the Fourth Amendment. A seizure occurs when “there is some meaningful interference with an individual’s possessory interests” in the property seized. [citation] Here, respondent voluntarily transferred any possessory interest he may have had in the magazines to the purchaser upon the receipt of the funds … An undercover officer does not violate the Fourth Amendment merely by accepting an offer to do business that is freely made to the public.
Id. at 469-70.