When representatives listen to what their constituents want and then use their own best judgment to decide how to vote, they are acting as .

When representatives listen to what their constituents want and then use their own best judgment to decide how to vote, they are acting as trustee.

Explanation:

When representatives listen to what their constituents want and then use their own best judgment to decide how to vote, they are acting as trustee.An important role played  by the elected representatives who listen to the constituents' opinions and then use their best judgment and come with a final decision.Also the Constituents elect their representatives as 'trustees' for their constituency.The quality of 'trustees' is that they have sufficient autonomy to deliberate and act in favour of the greater common good and the national interest.