public function whenBookOffered(BookOffered $event)
 {
     $bookDetails = $this->bookDetailRepository->getByISBN($event->isbn());
     $seller = $this->members->find((string) $event->selllersId());
     $book = new BookTransaction($event->bookId(), $bookDetails->title(), $event->sellersId(), $seller->fullName(), null, null, $event->price(), false, false);
     $this->books->save($book);
 }