I'd act very interested, get all the details, then just when they were salivating with greed, when they figured they had a sucker on the line, I'd say, "I have to go now, I'm working on a case."
"Case?" they'd say.
"Yes, " I'd respond. " I head the FBI's telephone investment fraud unit."
They'd hang up so fast. Didn't even say goodbye. LOL.