I have a TRU Shaymin and Movie Shaymin, both level 50, but the reason the level 30 looks legitimate to me is because of the Japanese Flower Paradise event. (Not available in other countries.) (Search "Flower Paradise" on Bulbapedia.)
I checked the date of the item needed to visit Flower Paradise, and it said it was Oak's Letter. (Search "Oak's Letter" on Bulbapedia.)
What impressed me and made me think the Shaymin is legit is that it was caught within the time frame Oak's Letter was distributed, April 18th to May 11th, 2009. The Shaymin was caught on May 2nd, 2009.
That's why I'm wondering if it's ACTUALLY legit, lol. XD Everything adds up perfectly, it's insane.