it all depends on the wealth and/or prestige of the buyer and the author.
if you are poor, then by all means do not think twice about getting books as cheaply as possible, e.g. library or used, or borrowing from friends.
if the author is rich and famous -- e.g. Donald Trump's autoboigraphy or yet another Stephen King novel -- then you, as an aspiring author who has not (yet) had the fortune to make it big, do not owe a damn thing to the rich and famous.
thus i speaketh.