unexpected arrivals

two weeks ago, I won this rather ornate silver direct pull corkscrew.  it arrived yesterday in its original box, and I was quite pleased.  well, upon taking it out of its box, i noticed something else wrapped in cotton; another corkscrew!
i emailed the seller, to ask him if it was a gift  or a mistake , and what he wanted me to do. 
He did say, it was a mistake, and asked if I would please ship it back…and, then asked how much I would pay to keep it.  So, negotiations have begun on the little mother of pearl and silver corkscrew…