I'll tell you the whole reason people do stuff like that.
as far as the person who had a magikarp asking for a legendary, he probably bred or caught one with insanely good iv's and a decent nature, so he wanted to clone it. If you make a successful trade, then the cloning fails, so they're actually hoping for nobody to take the offer. also, some people surprisingly do give up their legendaries and stuff just in search of stuff people are cloning. I had a lvl 100 palkia that I cloned 100 million times and traded it off to everyone. I thus got a tri-flawless shiny adamant magikarp, a jolly bellyzard, a lvl. 100 modest roserade, and tons of other useful crap. use the gts to your advantage and don't complain about it. it can only make life easier by allowing you to clone and trade worldwide
I will Eat Ur BRAINS!!!!!!!!!!!!!!!
also known as Stathakis on Smogon and Shoddy