The transactions usually took place in a car parked near West 166th Street and St. Nicholas Avenue in Manhattan. Abdul Davis would arrive from New Jersey, carrying guns in a bag, the authorities said. He sold them in batches of three or four: revolvers, semiautomatic pistols, shotguns, assault rifles.

All told, prosecutors said, he unloaded 82 weapons over 13 months in exchange for about $94,000, with the money wired to his bank account in advance. What Mr. Davis did not know was that his customer was an undercover police officer, and that the Manhattan district attorney’s office had obtained a wiretap on his phone.

On Monday, Mr. Davis, 52, and his girlfriend, Shelita Funderberk, 50, who is accused of helping him with the sales, were arrested in Linden, N.J., where they live, and await extradition. They are charged with criminal sale of firearms, conspiracy and other crimes, Cyrus R. Vance Jr., the Manhattan district attorney, said.

Mr. Davis and Ms. Funderberk could not be reached for comment because they were in custody in Union County, N.J., and had yet to be arraigned or obtain legal counsel.