I think it truly goes without saying that there are some niche markets that do incredibly well, some that do “ok” and others that just totally flop.
So what’s a safe way of choosing a niche market to promote?
The first place I would be looking is to see “how many people are actually searching those types of keywords”. If it’s getting searched a lot then you can expect to generally do very well promoting a product in that industry.
To find out how many keywords are being searched you can use this tool from overture for free here: http://inventory.overture.com/d/searchinventory/suggestion/
Just type in keyword or phrase that would most likely be searched in search engines and number that comes up beside it will be how many times it was searched in month before at Overture. To know how many times its been searched through Google you can generally multiply that number by 8 and you will get a rough figure of how many times it was searched over there.