eBay is ok for a good portion of what Amazon sells, but it’s not a perfect replacement. It’s not all auctions now. There are lots of things you purchase outright and they ship very quickly. Watch out for people who resell Amazon items at a mark up though. It too is not all that much better than Walmart, Amazon, etc, but at least you keep anyone from dominating.
Otherwise, sometimes there are small sellers you can find for niche products.