This is great if the inventory is there. I don't mind paying an extra couple dollars for a book; for me the reason I return time, and time again to Amazon is because I can reasonable expect to search for a book and have it ordered in less than five minutes.
Recently I have become more interested in buying used books online, and had success ordering from https://www.betterworldbooks.com/ and https://www.thriftbooks.com/.
I'll check this out if I am looking for something new.