The core theory is in fact quite simple: People have a (serious) problem to solve and the text presents the product as a solution to these problems by pointing out its benefits. In other words: People are expected to be self-interested.
Of course, potential buyers also wonder whether the product will deliver. Since media is not interactive, you have to deal with typical objections up front. Thus, these latters tend to be rather long.
Next, you'd need the attention of the audience. Thus, you make (lots of sub-) headlines that are easy to scan and makes readers interested. Among others, curiosity is often induced to make people willing to read the rest of the text. "Do you make these mistakes in English" is a classic example. The magic word here is of course "these". It promises an answer in the text without revealing it yet.
In the text, you can use typical sales tactics to overcome buyers' fear of later remorse. Caldini's 'Influence' describes the common 6 tactics.
For example, people tend to buy from people they like. One way to make people like the seller is to point out similarities. Thus, the seller often uses a profile similar to the buyers -- in the above example: "Natalie ('A Parrot Lover For The Last 12 Years')". This also establishes the seller as an authority -- 12 years is quite some time to gain experience and thus she probably knows what she's talking about.
Additionally, you have a clear call to action. For some reason, people are either unable to figure out what to do next or they are willing to obey commands.
And that's it, basically.
As far as I know there's no agreement about an explanation on why these tactics work. Why do people obey commands by authorities? You may construct an explanation based on the different models of economic or biological or psychological behavior.
But it's hard to test which of those (if any) is the one 'true' explanation.
Most people buy with their emotions, and use logic to justify the purchase. To maximize the number of people that get into that emotional buying state, you give out sales info in several different ways to cover most readers.
For something like a $79.95 ebook on parrot training, it would probably take you a fair amount of convincing to buy. That's why they give you a long list of reasons in storytelling format. If it were free, you would need less convincing, and the copy would be drastically shorter.
