iphone 7 10.2 ios cloud on

So bought iphone 7 plus for my wife's birthday. i received phone and it has icloud account already on it. seller refused to reply and if i try to deactivate icloud and delete from phone then it asks security questions. if seller had left his email on phone i could send reset request but now i must return phone and give no gift (plane leaves tomorrow) or try to return (hard if ebay not issue return soon or pay someone to do for me after im gone) i have read online there is diff ways to take the icloud off.. you can still use phone fine and its 256gb so no need icloud really but dont want the phone to stop working because the seller decided to be report phone lost or many things come to mind.