A friend of mine runs a larger-scale version of the used book business your wife used to run. She started out buying books from estates and old people looking to downsize. She'd take anything, paying a flat rate of something like 10 cents a book, and would show up at your house and haul away all the books. Then she'd list all the books on Amazon. Even if the book was selling for one cent she would make money on the shipping, since shipping costs slightly less than Amazon's shipping allowance (unless the book weighed over a certain amount and thus she'd lose money on shipping, in which case she'd recycle it, as she did with books in unsaleable condition). After a while she built bookshelves in her garage which let her store I believe tens of thousands of books, and hired people to do the book listing and shipping for her. She also moved on to more large-scale ways of acquiring books, like arranging with churches and schools to pick up the books that people left in their donation boxes. Every so often there'd be a volume that sold for $100, but the great bulk of the predictable cash flow came from making less than $1 for a large number of books sold each day.