HealthAmbition is a public case study website that was created by the guys over at AuthorityHacker.com. It's easily a 20K per month business based on their own admission, and they make their profit by display ads, recommended Amazon products as well as separate affiliate offers they push out to their mailing list. This has been a long term project owned by the Authority Hacker team, as they publish new content and test different monetization strategies.
Also, do some research on the opportunities in this market. What is the existing scene? Who is the competition? What data is available to tell you how lucrative this market is? The ease of selling will vary from market to market, as will the percentage of profits. Some companies may offer you a higher cut of the profit because their products are more difficult to sell. Determine what kind of selling experience you’d like to have, as well as the type of profits you’d like to see. Use those factors to inspire niche.
An affiliate agreement is when a company or an individual agrees to pay you for successful referrals. For example, Amazon has a massive affiliates program where they pay you a percentage of the sales you generate using their affiliate links. Affiliate marketing is everywhere these days. In fact, we’re able to offer our own Blogging Mentorship Program for free because Bluehost sends us money for every customer we refer.