Thank you for letting us know about the binding issue with your Starfinder Core Rulebook. Unfortunately, this is an issue we’re seeing more frequently than is typical for a normal print run, and we recently posted a blog detailing how we will be handling this issue. You can read the blog here: http://paizo.com/paizo/blog/v5748dyo5lk4w?Bound-and-Determined
Here is an excerpt from the blog, detailing how to proceed if you purchased the book from another retailer:
• If you bought it from a store, return it to that store by Friday, October 27. You should be able to get an exchange from them or reserve a replacement if the retailer is out of stock. They will in turn receive an exchange or credit from the distributor they bought it from, and the distributor will do the same with us. (We have already contacted our distributors regarding this issue, so your store should be able to work with them to address this issue.) If your store remains unable to help you let us know at customer.service@paizo.com; include the store's name and location so we can work with our distributors to ensure everyone is on the same page.
I hope this helps! If you are unable to have the issue resolved via your retailer, please let us know, and we’ll see what we can do to get you taken care of.