For a usual member to contribute a spell, they have to be a council member of a coven. The coven SpellCasters is one where you'll be promoted to council as soon as you enter. So, many people who contribute fantasy spells are a member of SpellCasters.
Use your common sense. Would a spell make you fly twice around the world with fluffy wings using a fairy dust? Or would any of these spells make you an immortal night creature who burns in the sunlight and is up there to suck on your blood? No, definitely they do not work.
Don't pay attention to the rating of a spell. You can see many 5 started fantasy spells when neither of them work.
However, if you want to be sure of a spell, cast one. Test it and you'll find out. But it doesn't mean if a spell says "drain yourself in the water to sell your soul to Satan and become immortal", you have to test it. It falls under the first section; Where you should use your common sense to decide.