One of the most efficient ways to determine if people are buying products in your niche is to take a look at ClickBank. ClickBank has thousands of products that people can buy.
The big drawback to ClickBank is you really have to dig deep to find answers. Their system can be difficult to navigate, but there is a nice way around that problem.
CB Engine offers a very effective way of bringing data to you for all ClickBank products. If you want to find out if people are selling products in your niche on ClickBank, CB Engine can give you results in only a few minutes.