Or sell the intro for 9$ and provide a link to the tome inside the book to your own payment processor.

That's probably against the "ToS", I would imagine.

Or “join my list for free X” in the cheap book, a email campaign which then promotes the upsell smorgasbord.

And get all your readers to shout at you for getting their readers to pay twice.

I can see how you might think that, but I actually really like the $9 100 page booklet and if I want to go deep, having the 250-500-∞ page book is something I would be willing to pay for in addition to the $9, maybe off a discount, but I don't think it should matter. I'd kinda like to be able to pay twice as it were and get condensed versions of books I already have.

I do understand that a shorter book might, and most likely does unless one has spent years thinking this way, take just as much or more effort than a longer book.

As @quickthrower2 mentioned, the email list. I like that, but unless I really want to follow something, I won't do email. What I am a sucker for is a cheat sheet or some infographic looking poster.

I will have to try it to believe it, but I agree there's a certain appeal to having a condensed version of the contents for less, so you can get the meat of the book, while you can get all the details and references and documentation etc. for the full price.

What I won't buy though are the first 3-4 chapters of the book to be met with the "insert card for more".

I agree!