Started in 1998, ClickBank is a go-between entity that connects vendors wishing to market their products and services, and publishers looking for relevant products to promote to their audiences. Whereas Amazon Associates is an affiliate program with a defined fee structure, ClickBank is an affiliate network that takes care of multiple vendors’ affiliate programs, so the commission structures vary. The vendors choose the commission rate, which is typically between 30 percent and 50 percent (though it can range from 1 percent to 75 percent). That’s significantly higher than Amazon rates of 1 percent to 10 percent, but of course, Amazon generates a much, much higher volume of sales.
The topic you choose must have enough depth that you can create a lot of content for it. This is important for building an authoritative site, for search engine optimization, and most importantly, for the end user. If you don't have enough content about a topic, you're not going to be taken very seriously as an authority on the topic and it's unlikely you can convince someone to make a purchase from you.