Ask HN: What is something you do for clients that consistently blows them away?
I never disagree with a client.  Even if I internally feel it won't work in reality, I always start my response with "That's an excellent idea you proposed, let me try if it works and get back to you". I come back after a day or two as to why the proposal won't work (if it was a bad idea to begin with) with sufficient data. Client is happy you that you considered his proposal and you've avoided a potential standoff that could've existed for the same duration !