Ah, research in the pre-LLM era was quite different. You actually had to know which questions to ask.
You get a much better response if you ask the right questions in the right language though. Expertise still has value.
I guess you just asked a librarian and hoped they'd point you roughly towards the right section and then just started to read random books?
You looked it up in an encyclopedia first, which gave you the basics. That gave you enough to find it in a library using the Dewey Decimal code. From there you could generally trust the book because they tended to be trusted if they were in a library. For newer topics you swapped books for journals.
Researching a niche topic as someone outside of the academic community with no journal access was basically impossible.
Encyclopaedias, damn I've forgotten that used to be a thing. I think I still have a few somewhere that were used maybe once or twice. Now that was something internet search engines really made obsolete almost overnight.
Come to think of it though, as long as civilization has existed, libraries have been a thing. Or well, monasteries or some kind of place that kept records and copied books. And before that you just asked the oldest person in your village/tribe and hoped they knew I guess. It's weird that access to knowledge has basically been unchanged for the past ~10k or so years until now.