I've returned clothes on Amazon and they told me just to keep it. I assume that's the equivalent of them just sending it to landfill. At least I can donate it to a local charity.

Also Zappos was clearly founded on the idea of ordering 3 pairs of shoes and keeping the one that fits. They say the returns go back for sale unless used and then go to charity/reuse, but happy to see other sources you have. I think a lot of that Zappos dna went into Amazon's policies.