I believe the best way to purchase books is from your local independent bookstore, or through mail orders from a slightly further away independent bookstore. (indiebound.org can help you locate bookstores, and some of my local favorites for mail orders are Red Balloon Bookshop and Subtext Books)
As part of my interest in routing book sales to companies that support booksellers and publishers, I provide Indiebound and Bookshop affiliate links on my book review posts. If you buy something using those links, I may earn a small commission, which goes towards supporting Programming & Pages through host fees and related costs. Thanks!