>The se are coming direct from a printer to Amazon and being sold in place of the legitimate inventory. There is no third party to go after here. There's only one seller in this case. That is Amazon.
No, it's not.
Even if it says "Shipped and sold by Amazon", it does not mean that the item originated from Amazon's purchase. Amazon considers co-mingled inventory as fungible.
Let's say Amazon has 10 warehouses, and every month, they order 100 copies of a book, and put 10 in each warehouse. Now, a third party seller comes onto the scene, and wants to sell the same book, fulfilled by Amazon, with co-mingling to reduce costs. To further reduce costs, he also only wants to send his inventory to the closest warehouse so shipping is cheaper. Let's say he has 100 copies of this book, and he sends them to warehouse 10. Amazon, seeing that there are 100 additional copies of this book in this warehouse, and knowing that demand is likely to stay relatively the same, knows that for the next 10 months, they do not have ship those 10 books a month to it. Now, Amazon has run through the stock they stored at warehouse 10, but they have an order from someone who lives down the street. They don't have any copies of the book that they purchased, but they have the co-mingled copy that should, in theory, be an exact copy of the original product. They then send it to the customer so that they have a shorter delivery time. If they were to ship all of the copies of the book that were sent to them by that seller, and had not replenished, when a customer ordered from that seller they could ship a copy from warehouse 3, but it would take an extra day to arrive. Or, someone who lives next door to warehouse 1 could order from the third party seller, but still get same day delivery because Amazon has a copy of the book there, even though it is their copy and not the seller.
This is what co-mingled inventory means. That all inventory is fungible, and it doesn't matter physically who sourced the item, as long as it is properly accounted for on the ledgers. That is fundamentally the point - you save significant costs and introduce real benefits to customers when you can ignore where the item was sourced from. The problems arise when not all of the sources for the items are good actors.
Looking at the No Starch Press Serious Python book, there are 41 sellers. I don't know how many co-mingle inventory or are FBA, but that means that any book sold that from any seller that co-mingles inventory (and items sold by Amazon directly are) can be fulfilled by items physically sourced from any other seller that also co-mingles inventory.