Anecdotally, I've started using Amazon FBA for things that I used to use eBay for.
Say I want a 2.2" ILI9341-driven TFT screen. That's not exactly something that you need everyday, so I could go to AliExpress/Taobao and get N for $3 ea in ~3 weeks, or eBay to get one for $4-5 in a lottery of anywhere from 3 days to 2 months. But now, I can get one from Amazon for $10 tomorrow.
It has prime shipping, which means you gotta figure they use the whole 'Fulfilled By Amazon' thing; I think that's like $3 a pop for small items. Heck, I was thinking of trying to make some money off of that kind of arbitrage, but it wouldn't be stable income since it's so dependent on a single 3rd-party company. Also, you'd literally be profiting off of China's sweatshop factories and lack of compunction around IP, which I feel sort of 'eh' about. At least using the things, you can argue there might be an end to justify the mildly shady means.
And it's just as likely to work as one from those other sources. If I wanted ethically-sourced reliable hardware I'd pay like $40 to get one with fast shipping from Adafruit. I really appreciate all that they do, but I also can't afford to ignore price for every purchasing decision that I make - and I am definitely not alone there, so there's probably still a lot of benefit to being "the everything store."