Not only Amazon, but the rise of ebooks in general. While there are still a lot of holdouts, I think every voracious reader in my family has switched at least some of their reading to ebooks. The ease of acquiring ebooks from the library through Overdrive/Libby means I treat the trip to the bookstore as an exploratory treat rather than an errand to buy the next book in the series

Amazon owns the most important aggregator of second-hand bookshops - AbeBooks. It actually helps me to support second-hand bookshops because I can search and buy from anywhere in the country. Sometimes after buying I develop a relationship and start talking to the shop directly.

BookFinder4U is even more useful, as it is a superset of Amazon, eBay, AbeBooks, and a few others. Coverage is not limited to North America. (http://www.bookfinder4u.com/)

viaLibri (https://www.vialibri.net/) includes ABEbooks and the other major US marketplaces (Amazon, eBay, Biblio, Alibris) and international marketplaces. It's far more comprehensive than bookfinder4u, which doesn't do well for books published before ISBNs were introduced (~1970).

Thanks, this looks like a good alternative. One thing though is that people may find the presentation of results easier to search through in BookFinder4U. For pre-ISBN books, you need to use the Out-of-print Search. I use it regularly to find old, limited run, academic monographs.