If I want to make a product in the chiropractic niche (don't really know what this niche is called) what data or metrics can I find, and where can I find them to determine this is a profitable niche? As an example there is a product on Clickbank currently that sells the formula to correct nasty forward head leans, which is a spinal/neck problem most of the time. How did this products' creators know this was a profitable niche, because at first glance, it wouldn't seem so. Or at least to me, because I do not know how to find the data which suggests otherwise.
This is question that can be asked across all niches. How can you figure out if the make money online via fiverr niche is profitable?