A key problem with the complaints is that customer reviews don't† take into account the effect of commingling. The expired food might have come from a different seller initially, but you were sent it because of Amazon's supply line optimisations. Amazon will know but when you write your review or read someone else's, you won't. Same problem as counterfeit goods and commingling though iirc there are more control in pl…
Commingling is bad, but does commingling mean they can't trace it back to which seller sent it to them for FBA? If they can, they can penalize that seller, not the other seller (who won the sale). I'm assuming Amazon has a unique id for every individual item in their warehouses. I'm not sure this is the case, but it seems likely given how their warehouses are organized and the location of stuff is very mixed up and o…
See also https://news.ycombinator.com/item?id=21244240, https://news.ycombinator.com/item?id=20549623, https://news.ycombinator.com/item?id=13952939, https://news.ycombinator.com/item?id=12062856
This comes up often.