Go up to some random guy with an iPhone, calmly take it out of his hand. Say: "I'll be taking this now.", and walk away.
Then you sell it.
You'd be surprised when it works.
haha... wear a black suit, tie, dark sunglasses and talk in a deep when you do this for an even more interesting effect..
but, ArrizX, good luck getting the extra cash.
(hooray, this is my 341st post!)