I have been thinking about this a lot since I saw the post.
I'm pretty good at selling thermometers. I know what makes a good one, (fit for purpose) and I know how to read the spec. (precision) I also know how to check them out (function). So when I write copy, I say, "its good for this job, is this accurate and should last if treated with care." So a customer has only to decide if they trust my expert opinion or not. They can judge precision, because its right there on the page. If it turns out to be a lie, they get their money back.
If I were to write my copy:
"Imagine sitting on a warm beach six months from now, knowing your time in the sun was made possible by the increased crop yield due to your astute investment in a thermometer"
Well, maybe it would work. But the customers I serve are generally pretty clued up about what they want, so they would all have to ring up before they ordered, to ask me "how accurate is it?"
I suspect many info products have to be sold on hype, rather than any precise information about content, merely because the sales letter is far more finely crafted than the product. At times there may be no product, just a sales letter leading you gently to the next upsell.
I do not think Dave's products are even in the same arena as the "residual monthly fees" matrix crowd.
I suspect the "Guru" crowd do not hold all the answers and could even be labouring under a burden of old data.
People looking to buy information products could well be just as savvy as the farmers who buy my thermometers. They want a way to measure what they are getting, with precision.