Is there any way to filter the available book results to exclude the Amazon/Kindle links? I would prefer to be able to check for used books listed by real people only.

When doing a search, you can input the name or ISBN, then when a list comes up at the top you can filter "Search Type" then select the list for "Posted" books. That way, only books listed as being available by members show up. There are other things you can filter for, such as hardback, paperback or Audio Book.

If you chose "All Books" you get both listed and unlisted. "Unposted" and "Wishlist" show those books that aren't available, and "PBS Marketplace" show those you can buy through PBS.

The Book Browser under Search lets you limit the searches.

Available books are color coded on the Author pages. Blue background for posted, Green for Market. And then, to confuse the issue, green links for posted.

They all will have a Buy From Amazon button.  That's just a link in case you want to order a new copy and give PBS credit for the referral to Amazon.  It does not mean when you press the Order This Book button that you will get the book from Amazon.  That link is just there to help PBS earn money and keep the sight free for it's users. The Order This Book button takes you to a PBS member.

If you only want to see books currently posted by other members:

After you do a search, go to the top of the gray search box and toggle the menu from "all books" to "posted books", and then click "update results."

But when searching "all books", for any listing, you can either click the blue and white "order this book" button OR you can click to add the book to your Wish List.  The first passes your order for an available book to another member.  Adding a not-yet-available book to your Wish List puts you in line for what a member posts the book.  It will be offered to the member who is first in the wish list line.

Every listing will either have a blue and white "order this book" button or a "+ wish list" button.  Either one involves swapping with a member, not buying from Amazon.