Anything by Malachi Martin is good.
There’s a few books by Montague Summers, the originals are expensive and they’re all risky. Summers was a bad guy.
There’s the book of abramelin the mage, which is basically a grimoire from someone who knew his stuff, where most of them are myth and fantasy. Again, not something to poke aimlessly at.
The Dark Gods, by Roberts & Gilbertson.
Oh, and Ouija boards are bad for you.
I have a work of Summers’ — his history of Witchcraft and Demonology.
I’m curious as to why you state that he was a bad guy.
I know he had a tendency towards embellishment, but is there something I am not aware of?