I was reading an article by Brad Sugars (founder of Action Coach International) on Entrepreneur.com last month, and he said something that has really stuck with me. This is not the exact quote, but pretty close:
"When building a restaurant it's not the quality of the chef, or the lavish decor that determines success. It's finding hungry people with money."
Note how how he mentions both "hungry and money".
I see a lot of small business owners who do both wrong. You can't sell your product to someone who does not want it, but you should also be careful of going after the customers who want it but can't afford it.
Look for niches that have money and need someone to feed them.