OMG you are not gonna believe my bad luck... I saw a Lvl. 100 SHINY Jolteon on the GTS and it wasn't an impossible trade. All that was wanted for it was an Aggron of any level. So I went to the cave by Drfitveil, caught a Lairon, evolved it, but when I got. Ack to the GTS, it said "Unfortunately this pokemon has been traded away to another trainer." 0.o
On the plus side, I got a good Aggron out of it. But I still wish I had that Jolteon...
I have a similar story. I was the Global trade and found I pokemon I wanted the trader only wanted a dexous; I had one! BUT the game wouldn't let me trade because my Deosous was a event pokemon!