>Some products come from AFN/FBA with an ASIN-formatted number on a barcode on the product bag, but which starts with "X" instead of "B". I believe this to be s

>Some products come from AFN/FBA with an ASIN-formatted number on a barcode on the product bag, but which starts with "X" instead of "B". I believe this to be some kind of inventory tracking code that relates the product to the vendor who shipped it into the Amazon fulfillment network. Correct. It is an FNSKU (Fulfillment Network SKU), which is both product- and seller-specific. Amazon listing for item with ASIN B1234567: * Seller 1 sells on the listing. His inventory of B1234567 is assigned FNSKU X8675409. When he sends inventory to Amazon, each unit must have a sticker with X8675409 covering the UPC code, or the seller can pay a fee for Amazon to affix the sticker. * Seller 2 sells on the listing. His inventory of B1234567 is assigned FNSKU X4894608. When he sends inventory to Amazon, each unit must have a sticker with X4894608 covering the UPC code, or the seller can pay a fee for Amazon to affix the sticker. For most listings, the seller can choose to use the UPC code instead of Amazon assigning an FNSKU. Called "commingling", this is unwise because there is no way for Amazon to distinguish between its own inventory, your genuine inventory, and another seller's counterfeits. Amazon says that its inventory procedures still differentiate between sellers, but a) no one believes this and b) all the stated procedures would do in a case of, say, Seller 2's counterfeit item being shipped when Seller 1 makes a sale would be to potentially identify that Seller 2 is the source of the counterfeit, as opposed to avoiding shipping it in the first place.