1 Lambert: Clearly the first step in finding this book Kyros wants is knowledge of where to look.
2 Lambert: That means we need a sage.
3 Mordekai: Well, let's see now... There's the Great Dragon Sage Ardaxar.
4 Lambert: Who Kyros killed.
4 Kyros: Hey, if he knew where it was, he might have got to it before I could.

I remember where I first learnt about sages. It was reading the Dungeons & Dragons Expert Set rules (page X21 of the old blue book with the wizard on the cover - available from D&D Classics as a PDF for just $4.99).

A sage cost 2000 gold pieces per month to hire, and was "an advisor, capable of answering questions involving great knowledge. For each uncommon question they attempt to answer there will always be a chance of failure. The DM will have to decide on the amount of time is takes and the cost of the research for each question. They are extremely rare and the DM may want to limit the number in a campaign."

That was the entirety of information about sages in the game. The Advanced Dungeons & Dragons rules would add much more explicit rules for determining cost, research time, and chances of failure for sages answering questions, based on the rarity of the knowledge being sought. But I kind of like this very open-ended "the DM decides" approach, which made the Basic/Expert D&D game much cosier in a rules-light way.

They certainly never mentioned the risk that asking a sage about some powerful magical artefact might incur the risk that the sage runs off and claims it for himself.