Anybody can start a good business with OK sales. However, to make sure you start a great business, with sales rocking, you need to make sure there is a hungry crowd ready and waiting for you. You need to find a niche that is small and focused enough for you to service it overwhelmingly well.
And you need to make sure that people in that crowd are ready, willing AND able to buy. There may be a lot less transactions than you wish if it’s an emerging market, so you have to see clear signs there IS a market. Once you find that hungry crowd all you have to do is give them what they want. And you will be rewarded accordingly.
There are several tell–tale signs simply by using Google that will identify whether money is being made in your chosen niche. Are people running ads? Are there are a lot of commercial sites on the first two pages?
If not, beware, your topic / phrase / niche may be very exciting but at this stage non–commercial.