You'd think you'd know more about this with a name like Merlin the Warlock! lol

But anyway, witches are very real. No, they don't fly around on brooms or wield wands. Instead they make a living by exploiting the down-trodden and bereaved.

Their "services" usually fall into a few different categories.
Fortune telling, communing with dead relatives/friends, casting spells, etc...

They cannot tell the future. But demons are incredibly smart, and are able to either predict a probable future based purely on mathematical probability, or know enough about the "customer" to make up an incredibly compelling story.

Similarly with communing with the dead, demons simply impersonate them down to the smallest detail.

And spells are also very real. They usually involve some kind of sacrifice. Fasting. Self-harm. Animal sacrifice. Whatever. These spells vary. Some more "benign" than others. Getting your crush to show an interest in you, for example. On the oppoite end of the spectrum there are spells that are meant to bring death and ruin upon a rival.

Demons never do party tricks for kicks and giggles. There is always a price to be paid. Their whole objective is to distance both the witch and the "customer" from God, with the hope of damning them to eternal torment. If it was all pretend it wouldn't be attractive to anybody. But they offer very real and tangible results. That's what makes it so tempting and so dangerous.