In an interview with a London-based newspaper, Conti, who is from Paisley, said he and a college friend sold encyclopedias door-to-door, which was "a great learning experience".
He said: "We were sent to no-hope areas and told to say such things as, 'Is a washing machine more important than your children's education?'
"Sometimes the door was slammed in your face, quite rightly, then we finally got a signature from these people could not afford this pointless encyclopedia.
"On the bus home we were both thinking that it was just wrong, so we went back and talked them out of it. It took us as long as it did to sell them the bloody thing."
He recalled his theatre job, in Glasgow rep in the early 1960s. He said: "One very foggy night the fog came into the theatre. We could barely see the audience. I think there were about eight people out there."
Conti said his best-paid film-acting job was a 1986 comedy entitled Miracles.
His co-starring role opposite Pauline Collins in Shirley Valentine, in 1989, was a "little boost" in terms of the fees he could command, and he receives "quite a lot" through residuals on DVD sales for the 2012 Batman film, The Dark Knight Rises, in which he also appeared.
Conti, who is currently appearing in a London production of Twelve Angry Men, said his best investment was his Hampstead home, which he bought 29 years ago. "It has gone up in value about 15 times," he said, adding: "If the Stalinist [Nick] Clegg ever got his desire for a mansion tax, we wouldn't be able to live here."