This is an outcome of what they have done in the warehouses to "optimize". Instead of requiring all of each vendor's items to exist in each warehouse they have

This is an outcome of what they have done in the warehouses to "optimize". Instead of requiring all of each vendor's items to exist in each warehouse they have commingled them (with what seems extremely little checks and balances). All items they accept for warehouse are tossed into the same bin location and any orders from any vendors for that item are pulled out of that random bin (instead of segmenting the vendors stock). In this way when your order Acme Widget A from vendor X you could be randomly getting stock from vendor C's items (which are knock offs), Vendor "acme"'s items which are the actual company items or vendor Z's items which they have setup to toss back into their stock from returns with little if any checking). This optimization provides warehouse "leveling" allowing Amazon to ship local products faster without needing to ensure each vendor splits tock or shipping via warehouse/warehouse but obviously builds in a huge carrot to game the system for vendors and makes it hard to have checks that identify the actual problem vendors.