I could not afford to buy all the books I read. I read many library books. Where does the library get their books? They buy them. When an author becomes popular the library purchases more copies of that author's books. I know my library has purchased several books because I requested or recommended them.
Susan Wittig Albert is a B level mystery author whose books I have read and enjoyed. I have borrowed some from the library and I believe I own a few. I will probably release the ones I own. Since she is a "series" mystery writer, perhaps the person who finds the books of hers I release will be inspired to buy others in the series. I can't imagine how that hurts her.
I have a couple bookshelves on here I follow, Harriet for one, and I make wishlists based on the books reviewed there. I know there are people reading my shelf too because they email me. I imagine some of them are getting books from their libraries or bookstores based on my review.
How does this hurt an author?