When to Say No to a Job

I heard a commercial the other day that said that the best words a contractor could hear are "I like your quote," and "you've got the job". For the most part, this is true. However, have you ever been in a situation when you dreaded hearing those words from the customer.
Maybe the job is very unpleasant, maybe it is bigger than what you want to tackle.
Recently, I had a customer who was having a buildup of water in her crawlspace whenever it rained. She had already discussed the issue with another contractor but she didn't like his diagnosis so she called me, this was the first red flag. After looking at the situation I suggested that rather than waste time and money trying to find out where the water was coming from that she install a sump pump in the crawl space to remove the water.
She didn't like this idea. She wanted me to completely redesign and rebuild the irrigation system in her backyard. I knew that this wouldn't solve the problem but I did the job anyway. Her backyard is bone dry now but she still has water in her crawlspace. A month goes by and she calls me again to come out and look at the situation. Again I suggest to her that she should install a sump pump in the crawlspace. Again she refused. Now she wants me to design a drain system under the house. I spent all day today trying to figure out how to do a job the wrong way!
Once I'm done designing and installing the drain system under the crawlspace, she'll still have some water there. Why, because she needs a sump pump installed. After she's paid me a couple of thousands of dollars and I've redone everything that can be redone in a crawlspace, maybe she will admit that she needs a sump pump. But maybe, just maybe, I should have just said NO to the job! Sometimes the headache isn't worth the money.