https://adwords.google.com/select/KeywordToolExternal Use that tool to check search volumes of numerology. Make sure there's enough traffic to make it worthwhile. Then search around the web to see if people are having desperate problems with numerology in their life, and if they're trying to solve those problems on forums and on answer sites (like Yahoo Answers). If they are, then there's probably a buying market. It's probably more of an interest/hobby market than a desperate need. So.. be absolutely sure that you offer something of value, and consider putting a controversial twist on it so that people already involved in the hobby will be interested as well as newcomers to the "science". If you get it right, you could pitch it similarly to "The Secret", which did very well indeed. For this sort of product it's all about the marketing spin you can put on it.