Booksfree.com?

It's the book world's answer to Netflix: for a nominal fee, Booksfree.com (misnomer: it's cheap, not free) will send you any of their 88,000+ paperbacks and audiobooks, along with a self-addressed, prepaid return envelope. Booksfree.com customers never need to worry about another human being seeing them buying a book that looks like this one--->

On the other hand, while the Booksfree.com website says that the company has been satisfying thousands of customers since 2000, I'm a little dubious about a site that has a header marked "Paperbacks Books".