(a) used books. As a Midwesterner I love that can directly order specific technology books (the ones everyone recommends), literally from a Goodwill in San Francisco, for the price of a good meal

(b) dodging Amazon co-mingling of inventory. Do I trust Amazon doing whatever it wants in a warehouse, or some eBay seller with a few years of built-up-reputation to lose but who specializes in the part I want? Let me tell you I have gotten a lot more handwritten thank-you-for-your-purchase notes from eBay sellers than Amazon. 3D printer parts, used computers+parts for the homelab, laser printer replacement parts, etc.

(Yes Amazon said they would stop recently... Not sure I believe it's fixed yet)