Well I'm not sure if this should go here or the general disscusion but I have compiled a uide on how to see if your Pokemon is Legit or not. Quite a lot of it is Common Sense but I still think people need to know, ok, so here it goes:
1. Was it a great deal?
If you got a great deal then chances are the pokemon is hacked, for example, I was on the GTS yesterday and saw a lvl 100 Shedinja being offered, in return they wanted a Spiritbomb, since I have about 20 (I often put then up on GTS for this like Mews) I offered one and when I recived the Shedinja I was amazed, It had about 100 in each Stat and was caught in a Master Ball, So the first rule is to stay away from amazing deals unless you can afford to risk them.
2. Location, Location, Location.
Check where the pokemonw as caught then compare it with Serebii's pokedex to see if it can actually be caught where it said. Simple enough and can help you catch a fake.
If the pokemon has abnormalley high/low stats then check its IV's with Serebii's IV calculator! If they are very low (3/2/5/2/6/1 For example) then chances are it is hacked, likewise if it has 31/31/31/31/31/31 then it is allmsot deffinatley ahcked as the chances of running into a wild pokemon with stats like that are 1 in 1.073.741.824.
If you are still unsure about your pokemon then check the pokeball it was caught in. For example, that Shedinja I mentioned earlier was caught in a Master Ball, Since it said it was Trasnfered from Hoenn I was unable to check the authenticity of its location, however, Shedinja is a by product of Nincada evolving into ninjask, and you MUST have a spare slot and a normall pokeball, therefore I know it was caught in the wild and hacked. Another thing is that people will do allmsot anything to hang onto there masterballs so if a pokemon comes with a master ball then presume it has been hacked (Unless you arranged for it to hold one) Only expect the running pokemon to be caught in Master Balls. (E.G. Lati@s, Cressalia)
5. OT and ID no.
OT (Offical Trainer) for event pokemon (e.g. Toys 'R' Us Mew's and the new Darkrai event.) will allways only be one trainer, for Mew I have two, Chance with an ID No. of 21246 and Mystry with an ID No. of 06930. So if your pokemon is very rare and was given away somewhere then check the OT and ID No.! I plan to get a list of all the OT and ID No.'s up soon!
Check the moves the pokemon you have currentley knows against the list it can learn on Serebii, if there is one your pokemon knows and is not on the list then it is most likeley hacked.
7. Trusty Traders.
If you got the pokemon from the GTS then I personally presume that it is un-legit unless there is evidance to prove otherwise. however when I trade with other people I ALLWAYS question them about the pokemon I am reciving, allways ask if they are Legit, If they are cloned etc and if they say they are unsure then point them in the direction of this thread and they can check.
Thats pretty much it for the moment, I will update it now and again and feedback helps a lot, also, if you have a pokemon that YOU have obtained from an event legitamentley (Like the Mew's from Toys 'R' Us) then please either post a few pictures of its stats (make then readable/visable though please) or post exactley what it says in the description, OT, ID No., The pokeball it was obtained in, The level it was obtained and the item it was holding (If any) and any other info you may want to include, and like I have said before, please only post if YOU YOURSELF OBTAINED IT! Not if your brother or your cousin or your best friend did but only if YOU did!