Once, a long time ago, I was writing a paper for my College American History Class and made the remark "and of course all politicians are crooked."
The professor wrote back, "Can you prove this?
The answer is no.
Therefore, I think you can apply the same approach to the question you posed. Do we really know that politicians only tell us what they want to hear?"
I would suspect that is true in many cases, because they believe they are acting upon the views of the majority that elected them.
Our task is to be more involved. I called my two Senators today. I talk to their staff members, about efforts to gut the Affordable Care Act. No one reading this may agree with me, but I have a right and obligation to voice my views. If I do not believe they are not being truthful with me, I will not vote for them. The problem we have, in my opinion, too many people still vote for the candidate belonging to the political party the individual voter supports, regardless of what the candidate says.
President George Washington, in his farewell address, warned about the influence of political parties on govermental decisions. I belong to no party. I am often on the losing end of an election, but I vote for the candidate I think is best. I voted against Mr. Obama in the first election. I voted for him in the second. I though he was lacking in experience the first time. The second time, I was impressed that he could get a divided congess to vote for the Affordable Care Act--lifesaver for me.
To more directly to answer your question, we vote because that is the process we use to select our political leaders. It is up to us to push for straight answers with warnings that if the answer is incomplete, you may not be able to vote for him. It takes time. Phone calls, letters to the elected officials, letters to the editor and working with your neighbors, but you can get a complete answer. It just takes a lot of work.