The easiest way is its objective. If a spell wants to do any of the following, it is fake:
> Cause you to fly, levitate, or make anything else fly or levitate, which cannot already do so on its own.
> Grow or alter limbs, appendages, or body parts in any way which they do not do so naturally
> Become anything other than human, to become half-demon, half-angel, a demigod, and so-forth
> Bring anything fictional to life, or summon anything fictional as an actual spirit*
* Some people believe in something called a thought form, in which an idea is given its own sort of autonomy, but still functions as part of its creator, though deliberately dissociated from the originator in function, until its purpose is fulfilled, and it is duly destroyed. In these cases, a thought form may be given the appearance or other characteristics of a fictional being, but the thought form is not that fictional thing; it is made similar in some aspects, within the mind of its creator.
> Change eye color or type (as in, "I want lizard eyes!" or, "I wish my eyes were brown in stead of green.")
> Make hair grow faster, change color or texture, and the like
> Force the free will of another. While this is somewhat debatable, a person can be influenced by certain means, but not forced simply by magic.
> Basically any -kinesis suffix ability.
Honestly, the list can go on excessively. Basically, if something cannot occur naturally, there is no chance of it happening via magic. Some things are absolutely debatable, and some which have even been studied by the government, which some people may call completely fake. But these things are more a practiced skill than something a person can just cast a spell and do.
That brings me into an entirely different tangent, of things which a spell doesn't do, because some magic or spiritualist-related practices are not abilities which ca be turned on or off as if flipping a switch, but are skills in perception.
A spell, basically, is sort of like a wish with a sort of ritual built around the desired outcome. It's a way to help push the 'fates' (for a lack of a better term at the tip of my tongue) in a favorable direction to one's desired outcome. Anything which does not have a chance without a spell is not really likely with one.
Prsona gave you an amazing list of how to do tell. I say just anything that sounds too good to be true such as prsonastated. Also what would help you is a book called 'Spells and how they work' by Janet Farrar that will help you determine what is real and fake, also would be a good idea to learn how magickworks. A bit of common sense helps as well.
Creating anything which does not exist.
For example, pyrokinesis, controlling fire, exists, but pyrogenesis, creating fire where there was none, does not.
You cannot summon anything without an existing chance of it happening.
Rain spells require clouds. Wind spells require air.
Any suspiciously simple curse has usually been created by a fluff. (Ex. "DEATH CURSE TOTALLY REAL IT WORKS TRUST ME XD" Spell: think "kill (person's name) satan" three times. they will die instantly.)
Shapeshifting spells. You cannot turn into a dragon. Trust me. Otherwise the world would be overrun with superpowered, omniscient, fire-breathing edgy twelve year olds.
Transformation spells in general. You cannot change the physical.
Another huge tell that something is not going to work, is a spell in which the poster concludes using something similar to, "Message me if this works."
Obviously the spell was posted by someone who has no earthly idea what they are doing, and are hoping to figure it out by taking shots in the dark, and hoping someone gives positive feedback.
Spells that change the physical world (fluff) is the immediate proof that something is probably false.
However most people follow the instructions to spells so much, they worry if they did it right. These doubts in turn set up the spell for failure. Sometimes showing the universe your desire is enough to make a spell work.
Be mindful of unapproved ingredients as well in spells.
Generally - fluff aside - the instructions give it away. Things such as extreme simplicity, poor spelling and/or grammar, etc should be approached with caution. Do your homework on the spells, and keep in mind that no spell within reason works as well as the ones you create yourself.
I have been browsing on this website, among others, for some time. Although I am a newbie in as much as I have only just joined this site I am not new to the ways of Wicca. I have been practicing Magick for many years now and I have to say that in relation to fake spells it does seem that a lot of the people posting their spells on here are either making fun of the Wiccan way or, which is worse, actually believe that their spells work. Just because you add the words "So mote it be!" to the end of something this does not make it a real spell. As has already been mentioned by Prsona if it is not natural it is not real. I would just correct one statement that he made, it is possible to change eye colour. Certainly he is right in what he says about type, but it has been proven that by force of will people can change their own eye colour so I would say that Magick would also be able to do this.
On an additional note, fake spells aside this is one of the better sites I tend to hang about and would like to say thank you to everyone for all the invaluable information I have found here over the years
