But who vouches for the author? If you're not already experienced in the domain, how would you know whether to pick up a book written by Jane Expert or by Dave Dunning-Kruger?

Traditional authorship is self-vouching: writing a coherent book on a complicated subject is hard. You can't exactly bullshit your way through 500 pages of car maintenance minutia. If a book actually manages to make its way all the way to a book store, there is a pretty good chance it is worth reading.

LLMs change this equation. Any idiot can prompt an LLM into writing reasonable-sounding slop, so any idiot can now write a book on any subject. Combine that with self-publishing and print-on-demand, and suddenly all bets are off.

If 99% of LLM-written (or LLM-"assisted") books on a subject are garbage you aren't going to buy a book and hope it is the 1% - it makes far more sense to save yourself the money and get the mediocre answer by prompting the LLM yourself. Want expert information? Just buy an LLM-free book written by an actual expert.