Not for an entire career, no. Sanders was taking politically unpopular but righteous positions since day one. He has preached the same message regardless of what would be popular or potentially make him money.
Cynicism and skepticism have to be balanced by a willingness to actually examine and parse the facts in front of us. I don't agree with Sanders on everything, but there is no evidence that he's faking his sincerity.
Oh, my bad lol