I've decided on an iPhone 5s specifically, 16g, 32g... i don't really care, but i do need it unlocked, as i intend on pay as i go, not a plan. Aside from the obvious (damage, shady back-alley meetings), any tips on how not to get screwed? I'm no idiot, but i am new to phones and i don't want to buy something stolen, damaged (that looks nice), or unusable for other reasons. I'm looking for a black/space grey 5s, as new as possible, and i'll want the box and all the factory stuff that comes with. There seems to be quite a few to choose from, starting from around $250 for aesthetically damaged and locked-in, and up to about $450 for 10/10 unlocked, pretty much new phones. Anything i should know?