A big deal with this may be due to upbringing and what part of the country/world you come from. While part of me dreams of being able to do this kind of work (I’m the exploration type), I can’t, since I can’t drive, limiting my searching ability. Regardless, my background keeps a nagging sense of impropriety of arbitrage in my mind. To my parents and my childhood role models, it’s not “real work,” since it neither creates anything new or abides by the “sweat of your brow” requirement my more religious acquaintances would demand.
TL;DR: I believe in “work smarter, not harder,” but most people I know/knew believe in the opposite.
It does create something new, it creates value. I'm amazed at the 'arbitrage is bad' comments, I can't remember seeing it anywhere before. Someone who finds a buyer for a thing that couldn't be sold before (i.e., was worthless) creates value by enabling the transaction.
It creates a new opportunity for the seller - those individual books were previously not available online. they were just sitting in a bookshop.
Finding these books, then placing them online, and handling the shipping to the buyer is certainly adding value.
TL;DR: I believe in “work smarter, not harder,” but most people I know/knew believe in the opposite.