“I placed the substance in water,” he wrote. Plopping and fizzing ensued. The powder caused the water “to bubble like Alka-Seltzer,” the officer wrote, adding: “I know based on my training and experience that cocaine does not react in this manner when mixed with water.”

Whatever disappointment the man seeking drugs felt upon realizing he had been duped and how close he had come to snorting cold medicine was presumably offset by the relief — and oh, as the jingle goes, what a relief it is — of being free to go. Mr. Saho was not quite as lucky, but almost: He was charged with lesser offenses than selling cocaine, including a misdemeanor charge of possessing an imitation controlled substance and another of fraudulent accosting. He accepted a deal under which the case would be dismissed in the future if he stayed out of trouble.

It was not an isolated incident. On Feb. 2, the police arrested a 51-year-old man, on West 46th Street, who was carrying marijuana but who told officers, “I sell fake cocaine,” the police said. And on July 24 at 4 a.m., a suspect who offered to sell a stranger cocaine was arrested and admitted the drugs were fake, according to another criminal complaint. This time the substance was the pain reliever BC Powder.

“Aspirin, baby powder, talcum powder,” said an employee at Lace Gentlemen’s Club on Seventh Avenue near West 48th Street. The employee, who declined to give his name, said he had seen many fake-drug deals conducted outside the club. The dealers seem to be targeting the club’s customers, who are, rightly or not, believed to be tourists who are gullible and have cash in their pockets.

“Old-school stuff still works here,” the employee said. “They’re blatant. If you’re standing around outside, they’ll walk up to you.”