I am describing people, not repeating people's self-descriptions, and since I am claiming that people are systematically mistaken about their self-descriptions, of course there should be a disagreement between them!

I'm complaining about your terminology. Terminology is about which meaning your words communicate. Being wrong about one's self-description is about whether the meaning you intend to communicate by your words is accurate. These are not the same thing and you can easily get one of them wrong independently of the other.

I think you do care more about the price than about the reviews? That is...

The sentence after the "that is" is a nonstandard definition of "caring more about the price than about the reviews".

That's fighting the hypothetical.

I don't see why you think that.

It's fighting the hypothetical because the hypothetical is that I do not want to pay $5000 for a book. Pointing out that there are situations where people want to pay $5000 for a book disputes whether the situation laid out in the hypothetical actually happens. That's fighting the hypothetical. Even if you're correct, whether the situation described in the hypothetical can actually happen is irrelevant to the point the hypothetical is being used to make.

but if your point is "people don't do weird thing X"

My point is not "people don't do weird thing X", my point is that people do not use the term X for the type of situation described in the hypothetical. A situation does not have to actually happen in order for people to use terms to describe it.