Customer Development is a process that's really meant to be applied to prospective customers. The whole point is to figure out what problems the market needs, and ultimately what kind of solutions there might actually be a market for.
Instead of building something and then going to people and asking if it's useful, find out what a large segment of the market would find useful first.
Get out of the building and talk to actual people - create simple experiments to help you prove whether a market actually exists. Validate your assumptions before building. Follow the Lean Startup methodology :)
Nobody is going to tell you how to do it. it has to come from you.
-Vincent Van Gogh, hypothetical
Starry Night (Value: est. ~$80M-$100M+)
Vincent Van Gogh, Actual
On the other hand, steve jobs didn't need to ask his customers how they'd like an iphone - he told them why they'll like it.