I was conversing with someone who does tarot cards, and I essentially asked "why should I buy any of this". Their response was interesting - their theory was that our subconscious is a lot more impactful than we realize, and that, for a tarot card reader, their subconscious aware of the cards, the meanings, and where cards are when we shuffle them, so a reading is more about tapping into the subconscious than it is anything supernatural, mixed in with a hint of being subconsciously "in-tune" with the universe.

I still don't fully buy it, but I thought that was an interesting theory, and I think there's some truth to it. My personal theory with that stuff is, sometimes all you need is a metaphorical landscape to find meaning that you're looking for. So, as much as I think astrology is complete BS, I think it could actually be helpful for some people.

I could imagine something similar happens with Ouija boards. There's probably some level of subconscious coming into play, some level of "searching"/being open to meaning, and (usually) a lot of fear mixed in.

And as far as bad things happening post-reading, I feel like it's similar to buying a car and suddenly seeing a ton of that car around town.

Just my two cents.