Something unpleasant is coming when men are anxious to tell the truth.

Sudden eagerness for candour is usually a signal rather than a virtue. When somebody announces they are going to be honest with you, the honesty is generally in service of something they want to deliver, and the framing is there to make it hard to object. Real truthfulness tends to be quieter and less announced.

Listen for the preamble. When a conversation opens with a claim about how frank it is about to be, brace gently and stay curious about what the frankness is for. And notice when you do it yourself, since the same move usually means you decided something in advance.