The most sure fire way of vetting an idea like this is to talk to the folks you imagine using this product or service.
For example, if your service helps widget buyers find and purchase the finest widgets of the world; strike up a conversation with those buyers and talk to them about the struggles and frustration they have with buying widgets.
Then introduce your idea, "Would [my service] help you find better widgets? What would make you say, "WOW! This is what I need.""
Good luck! I'm happy to help you further with this process. I'm working with a number of entrepreneurs right now who are in various stages of vetting their own ideas for services.