NEW YORK — When dozens of former police officers and firefighters sought disability benefits, advisers provided a playbook for faking mental illness — how to describe daily routines of languishing dysfunction, flunk simple concentration tests convincingly, dress down for benefits interviews, even how to link their supposed symptoms to 9/11, prosecutors say.

The decades-long scam netted more than $20 million in Social Security disability payments for more than 100 people and tens of thousands of dollars in kickbacks for the benefits experts who helped them, the Manhattan District Attorney’s Office said this week in unveiling a case that points out the complicated role consultants play in a system that helps sustain more than 10 million people nationwide.

Experts say advisers can give people valuable help in understanding what’s needed, compiling information and navigating bureaucratic complexities. But they acknowledge the boundary between explaining and gaming the system can be tricky, and sometimes crossed.

“A lot of times, a person really does need a lawyer or someone to guide them through the system. But once you have that, they have a financial interest in the case succeeding,” says Dr. David Reiss, a San Diego psychiatrist who has evaluated first responders and other applicants for disability, workers’ compensation and other benefits. At times, he thinks consultants’ conduct begs a question: “Where’s the line between helping someone to express what’s going on emotionally, and where is it planting seeds?”

In the New York case, benefits advisers Joseph Esposito, Thomas Hale and John Minerva and lawyer Raymond Lavallee are accused of supplying a veritable forest of fibs.

Many applicants had physical injuries that qualified them for police or firefighter disability pensions but not for federal disability benefits that require being unable to work at any job for at least a year.

Esposito, a retired officer who’d told applicants to claim psychiatric problems stemming from their work.