There was a joke going around that said you hired a consultant to tell you the time, he asked for your watch, told you the time and kept your watch. Whenever I heard that I added that before I left with their watch I taught them how to tell time.
There is always a message in these jokes. I think many times the client really know the solution to the problem but for many reasons needs another opinion. If in the process you can give him the necessary tools to solve the problem himself next time as well as working thru the solution with him this time, that is really good consulting I think.
Then I think you have the potential for a long term relationship which is the secret to successful consulting. If you come in like the Lone Ranger and solve the immediate problem with no learning, you will disappear as quickly as the Lone Ranger.
How is that for lots on metaphors!