While we are always working to improve our system to make sure we are estimating the proper weights on packages, we understand that sometimes the final package may weigh more than what is on the provided shipping label. In these cases, please contact our support team through the chat feature at the bottom right of this page or by emailing us at support@pangobooks.com with the name of the book (or books) in question and the updated weight of the package. We will be able to provide a new shipping label at no added cost to you or the buyer.