The caseback looks good, but the bezel, dial and buckle look a bit funny to me. It could be a non-US model or it could just be the photos, but based on the fact that the owner does not know either, I would stay away unless he can produce the papers. I have seen someone who inherited a Patek who was so exited to put it at auction and the watch was 100% fake and worth about $2. Always trust your instincts.