In general, I'm disappointed how Amazon went from being a store to a "marketplace". Sometimes I want to buy somebody who'll actually curate their list of products and has a reputation to stand behind that they don't want to sully by selling garbage or price-gouging on items they don't normally stock.
I buy a lot of used, old, obscure things (mostly books). Very often, Amazon is the only place I can find it reliably; my other options would probably be asking my Japanese/German/etc friends to dig through second hand shops and mail it to me.
I love the Amazon marketplace. (I also hate the 3rd party seller feedback emails but I have strict email filters so who cares)
The marketplace works out very poorly if one doesn't have Amazon in their country. The info about shipping abroad is very much buried into whatever, and Amazon IIRC mandates that purchases can't be combined: if I buy two $0.01 books, FROM THE SAME SELLER, they will be shipped separately at $4-6 shipping & handling each.
It's not that I think the Amazon Marketplace is a bad idea, it's that the way the Amazon Store and the Marketplace are conflated by Amazon that's the problem.
eBay and AliExpress do what Amazon Marketplace does better than Amazon Marketplace, but Amazon wins because they've leveraged their success as a store for it.
If you are interested in books from the German-speaking region you should also take a look at zvab.com (now owned by Amazon) which is the largest marketplace for professional used book sellers.
But maybe that's just me.