Amazon is kind of a third thing though. They're a warehouse in addition to a marketplace like eBay. If you buy a thing from an auction site and it's defective, the site might be able to get you a refund (or not, if you didn't pay through them), but they can't get you a replacement product unless the seller has one. The site has none to send you.
Amazon will send you another one, possibly from a different seller. That's... weird. It's like they inverted the model where the wholesaler sells to the retailer who sells to the customer. Instead the retailer sells to the customer through the wholesaler, combining different kinds of products into a warehouse instead of splitting up a warehouse with large quantities of the same product into smaller retailers.
But you still want to put things like this on the "retailer" because they're the one who knows anything about the product. It's the same reason you don't put it on eBay or UPS or a self-storage place. And the same reason you don't need to -- you want to shut down or punish the retailer selling the fraudulent product, not all the other retailers or the surrounding infrastructure providers.
Walmart is not a 'marketplace', yet they could easily give you a replacement product from a different 'wholesaler', just like Amazon can give you a replacement from a different 'retailer'. There is no material difference here. Amazon owns everything about the interaction, they have just creatively outsourced creating product listings and a bunch of product risk.
Amazon will send you another one, possibly from a different seller. That's... weird. It's like they inverted the model where the wholesaler sells to the retailer who sells to the customer. Instead the retailer sells to the customer through the wholesaler, combining different kinds of products into a warehouse instead of splitting up a warehouse with large quantities of the same product into smaller retailers.
But you still want to put things like this on the "retailer" because they're the one who knows anything about the product. It's the same reason you don't put it on eBay or UPS or a self-storage place. And the same reason you don't need to -- you want to shut down or punish the retailer selling the fraudulent product, not all the other retailers or the surrounding infrastructure providers.