Misleading free download ebook

This afternoon I helped a student to locate an e-book through Internet. I noticed that event though the links say free download, the book  is absolutely NOT FREE. Readers will have to register and sign in and pay a certain amount of fees to access the e-book. If it is the general practice, why so many links say "free download"? - Misleading and ... make readers frustrated. You thought the download is free, yet as soon as you click on the link, you will be asked to registered and pay for the download. ("sigh")