Create a landing page, put it up on forums like hackernews, reddit, quora and see what kind of conversion rate you get for the concept alone. Talk to people.
I really like Unbounce for building landing pages. Unfortunately Google refuse to run Adwords campaigns for them though, which is a shame.
I could understand if it was just a lead gen site collecting e-mail addresses, but I was selling a gift product, with product photos, plenty of info and secure payment processing too. So who knows! I've completed the form to get them to re-review the site but I doubt they'll do anything.