This is not true. They offer a service where they will add an FNSKU label to your products for .20/unit, which will mean your items will not be co-mingled. But as a seller, you can also apply the FNSKU to the items you send in and not be charged the additional .20/unit. It's up to the seller how they want to do it, but it's not a mandatory charge, just a convenience if you want Amazon to do it instead of yourself as the seller.