Among other things, I’ve fallen down a Black Tapes rabbit hole, and found this comment on a BT subreddit: “The rare books lady DEFINITELY creeped me out. You would think someone with such occult interests would have enough respect for the source material to not blurt out every demonic spell in the book.” (by Sharkfishhead)
And now I can’t stop imagining an old woman puttering about an occult shop, fascinated with occult material, but also skeptical, even though she’s summoned and/or dealt with enough supernatural stuff that she should be a true believer. Maybe a little Granny Weatherwax, a little Miss Marple, a heaping cup of the harmless old lady trope with just a soupcon of the evil old folks cliche (or maybe “dangerous” rather than “evil”).
Fat, and her clothes are maybe a little raggedy, she seems like a total feather-brain, and she always has cookies or sweets loose in her pockets – but she’ll not hesitate to slit a throat that needs it, and then smile sweetly at any shocked bystanders, “They WERE evil, dear.”
And then it turns out there’s a network of the sweet old arcane dears, and they have meetings and keep in touch, and not infrequently Agnes will visit to help with those beastly cultists, “You remember Agnes, child, she knit you that sweater with the cables on.”
ETA: I just realized I basically want something very like the series John Bellairs has already written. Ha.