“That is the modus operandi of a spy, not an informant.”
Halper was a professionally trained spy, in the pay and under the orders of a world-class spy agency, conducting classic HUMINT spy operations.
What actual spies do to gather Human Intelligence, is recruit sources who have access, and then manage them. There is a large element of grooming and psychological manipulation - targets are typically assessed by teams before being approached, to determine what would be most effective at controlling them (flattery, blackmail, bribes, ideology, etc.).
The professional spy (case officer) is the handler, the people on the inside are the assets/informants.
Halper came at his targets with a typical broad array of spycraft tools, appealing to their ambition and egos, greasing them with nice trips and lucrative side jobs, buying the drinks and bringing a honeypot woman (Azra Turk, whose image seems scrubbed from Google). Professional spies typically seduce their assets.
The recruiting and manipulation power of this classic spycraft is such, that even those serving life sentences for spying, still like their handlers personally. People are seldom catered to by such broad spectrum psychological gratification, as that provided in a tailored package designed by a world class spy agency.
And let us not forget Halper's past forays into 'opposition research.'
From Wikipedia:
In 1979 he became National Policy Director for George H. W. Bush's Presidential campaign and then in 1980 he became Director of Policy Coordination for the Reagan- Bush Presidential campaign.[7] In connection with this position Halper's name came up in the 1983/4 investigations into the Debategate affair, which was a spying scandal in which Central Intelligence Agency (CIA) officials gave inside information on the Carter administration to the GOP campaign. Reagan Administration officials cited by The New York Times described Halper as "the person in charge" of the operation.[8][9][10] Halper called the report "just absolutely untrue".[11]