When 'No' is the right answer to give a customer

We recently had a customer who wanted an attic/roof fan to help keep her top floor cooler (they work great!).
But her house would not have benefited from the fan due to house's layout.  So, we suggested instead to have a good Vornado-brand fan, and a window air conditioner.
She really wanted an attic/roof fan and asked about different ways to do it.  And we felt bad saying 'no' because we knew she was disappointed.
Hopefully, after she has her fan and a/c unit, she'll appreciate that she's saved money and got what she really needed.