It's true, It's risky trading for legit pokemon like shines or legendaries of EV trained pokes, but I always 'summary' the pokemon I'm trading for right before I trade it to check it's location/level it was caught in, possibly It's ID if it is an event and if It was imported or not. =)
That's why people should clone, even if it were against their principles. If you lose a valuable shiny/event, it's your own problem. Although I'm not a great supporter of cloning, it is only good that people found out how to do it.
And if a Pokemon is well hacked, you don't see the difference right away.