I am a fairly new member and was looking at a book on this website today and noticed it was for sale.  I was not aware that you could buy books here.  I thought they were just swapped.

If a book is not currently available in the system, there is a button to buy it new. This usually takes you out to Amazon where you can purchase the book and PBS get a little bitty commission on the sale. It is not members selling the books, you are correct that swapping is all that is allowed here. If you are not in a big hurry to get the book and want to wait until it becomes available you can hit the Wish button and that will put you in line for the book on PBS. You would be able to see where you are in line after you've added it by going to your WL tab and hovering your mouse over the grey (!) on the book.

Welcome!!