The buy it new button is not on every book, only those that are not currently available for swapping. Yes, you can buy a used copy if you click on the button. You get a list with all the available prices. It's o.k. to click the button and see what's behind it, you can easily cancel out.

I think PBS does get a cut of any sale that goes through Amazon, not just the ones from Amazon itself.

I just wish that I could keep adding items to my cart after putting one in.  Right now, it looks like all I can do is buy one item, them move on to the next and buy it.  Buying them separately keeps me from buying several at once or combining the books I link to through PBS with other items available at Amazon that are not available here - DVDs for example.

Oh well, can't have everything.

PBS does get a small amount of each purchase from the Buy It New feature. Per the Help Center it is 'tiny, but every little bit helps. As for adding more than one book from your wishlist, if you choose "Back To Previous Page" you can choose the "Buy It New" button on other books and it will add it to the same cart on Amazon. I did a multi book order from my wishlist this week and since it was over $25.00 I got to choose the free shipping option at check-out, but yes, you can not add items that are available here at PBS, or search for other media to add to your order. It probably has to do with the percentage of the sale PBS gets for referring members.