Here’s a good example of how lead sales can work in real life: My second website, Life Insurance by Jeff, brings in a ton of traffic from people who are searching the web to find answers to life insurance questions. While I used to have the website set up so I could sell these people life insurance myself, it was a lot of work to process all the different requests and clients. As a result, I started selling the leads I gathered instead.
Sometimes, individual entrepreneurs with great products are worth a look, although you should check them out first and do some research. Entrepreneurs or companies may run their own affiliate program and you can apply directly to them to promote their products and services. Finally, Amazon is always an option as you can be an affiliate for just about any type of physical product on their network.
If the answer to each of these questions is a resounding yes, rather than jumping to conclusions immediately, take time to research whether or not others are out there making a sustainable affiliate income from products and content in this niche. In a sense, competition is a good thing here—it'll help you validate your idea and prove that it's worth of building a business around.