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.

> I buy a lot of used, old, obscure things (mostly books).

I find AbeBooks to be very good for that. Ironically, they were acquired by Amazon, but they are still a separate system.

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.