You see the person you wondertrade gets the pokemon and not you. There are rare occasions when you can trade it back or you get the pokemon you wondertraded, but it's very rare unless you wondertrade common pokemon. The best way to get reliable trading partners are forums like here or ask close friends.
In other news, I caught a shiny venomoth in friend safari. I was actually looking for shiny gloom, but ended up getting one in GTS.