I guess this is the reason people do market research before they start working on it and market research depends on targeted audience. If there is a website existing that might not be reaching to your targeted audience. So the best way is to identify your audience/customer and try to approach them.
I was about to start working on an idea since it was fascinating for me, but I called my friend to do a market research and people liked the idea too. But every one had a common problem and I was not able to address this problem.
So get someone who can reach the targeted audience and can come up with feedbacks as well. The best way to do this is to find Business students looking for research/survey ideas so they can prepare reports as well. You can approach a college student or institute and see if they are really interested in researching your idea. They can do a lot of research and you will land up with real time results and feedbacks.