I don't believe this to be true. SBA in theory has it's own "pile" that they can of course use to substitute with a FBA third party seller if they deem it cheaper as they are confident that they are substituting like for like.
Given how FBA items are labeled differently (the Amazon required ASIN sticker) than SBA I can't recall a time I've received a third party item when buying direct from Amazon. I also can't really say with any certainty it does not or did not happen, but it was not obvious at least.
I've also seen contracts the explicitly forbid the co-mingling for brands that sell direct to Amazon. By necessity these would need to be under different piles on the backend - and it's easy to see different ASINs for the same SKU by searching for common big brand items. There will be a SBA listing, and then many other listings gaming the qty/size of the item that are FBA. An item that comes in the same size and packaging often is listed twice (or more) times with one being SBA and the rest third party.
It's definitely clear as mud, but I think the "sold by amazon/fulfilled by amazon" being co-mingled is largely urban legend. It's all speculation like this thread here, and very few verifiable facts when you dig into any of the reporting/social media accounts. I'm 100% sure it happens by mistake and very well may have happened as routine business in the past, but these days I cannot come up with an example that shows this happening on any scale.
I don't believe this to be true. SBA in theory has it's own "pile" that they can of course use to substitute with a FBA third party seller if they deem it cheaper as they are confident that they are substituting like for like.
Given how FBA items are labeled differently (the Amazon required ASIN sticker) than SBA I can't recall a time I've received a third party item when buying direct from Amazon. I also can't really say with any certainty it does not or did not happen, but it was not obvious at least.
I've also seen contracts the explicitly forbid the co-mingling for brands that sell direct to Amazon. By necessity these would need to be under different piles on the backend - and it's easy to see different ASINs for the same SKU by searching for common big brand items. There will be a SBA listing, and then many other listings gaming the qty/size of the item that are FBA. An item that comes in the same size and packaging often is listed twice (or more) times with one being SBA and the rest third party.
It's definitely clear as mud, but I think the "sold by amazon/fulfilled by amazon" being co-mingled is largely urban legend. It's all speculation like this thread here, and very few verifiable facts when you dig into any of the reporting/social media accounts. I'm 100% sure it happens by mistake and very well may have happened as routine business in the past, but these days I cannot come up with an example that shows this happening on any scale.