This assumes it is really that simple. You are adding a manual, human process. Humans make mistakes. Humans can intentionally make mistakes. Barcodes fall off,

This assumes it is really that simple. You are adding a manual, human process. Humans make mistakes. Humans can intentionally make mistakes. Barcodes fall off, get defaced, etc. Those barcodes, hardware and software require money and up-keep. The humans receiving the products also can make mistakes and return the "wrong" item that happens to look the same (this is a source of counterfeits, even at Walmart/Target). And then we get into the shipment chain. Counterfeit swaps happen during the transit of packages to the warehouse and to the receiver's home. This is a really, really hard problem. And to be able to do it in a way that doesn't substantially raise the prices of the products only complicates that more.