Offering your book for sale directly on your Web site can provide the highest profit margin. For those who sell downloadable books from their own site, the sale price is nearly all profit, excepting credit-card fees.
But many authors who sell directly on their Web site also offer a range of other options, like buying links to Amazon or Barnes & Noble. Some people are just more comfortable buying from a familiar merchant like Amazon. Authors who want to encourage sales through their own Web site can do so by offering something a bit extra, such as signed books or free shipping only for direct sales.