> It's non-authoritative, clients can slap a "cannot verify this value, check the price on the next step" sticker on it as necessary.

Because users are well known for carefully reading and following instructions, rather than just going ahead and hitting the OK button without hesitation.

This isn't a solution, it's just a way to remove responsibility and then blame the user - "it's your own fault for not reading, you were warned" - which may be correct, but it's entirely predictable and shouldn't be encouraged through bad design.