How to authors verify how many copies of books are sold?

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Generally the copyright rules all across the world are the same. Authors of books in majority of cases get 10% royalty for writing every type of books, whether books of law, science, literature, or any other subjects. In addition if there are electronic version of the books, then royalty is there for sale of those versions. But only publishers have the record of the number of books published and the number of copies sold. In majority of cases a yearly report is given to the author about sale of the book. But how do authors know how many copies of the book are sold? Is it not possible on the part of the publishers in not giving accurate records?