Fake spells

I think the easiest way to decide is a spell real or not is to think of can that desired result happen any other way than magick.

For example - it's a love spell, someone will fall in love with you. is it possible for a person to fall in love with another person without magick? Yes, it could happen. So that can be real. And I'm not justifying the use of love spells, just giving an example and this is what first came to mind.
But, a spell that promises to turn you into a mermaid. Could you be turned into a mermaid without magick? No. Then magick can't help that either.

I think that's enough to figure out if a spell is real or not.