They just use it to inflate their catalog. I have a list of sites that I get my public domain books from, like Gutenberg, that I know are at least clean and not bad scans or partial books. B&N classics (their in-house line) are pretty cheap and they're reliably edited and formatted and annotated--if you want that, they're worth the money IMO. I really don't mess around trying to get free public domain stuff on the big retailer sites.
Here's their version of Franklin's Autobiography: like the others, it's $3.99
http://www.barnesandnoble.com/w/auto...=9781411428218