Commingled Inventory: How Someone Else's Unit Becomes Your Used Sold as New Complaint

What commingling is

When you send stock to FBA, Amazon has to know which unit belongs to whom. Under the old setup there were two ways to do that, and the choice sat on a settings page most sellers set once during onboarding and never looked at again.

The first option is the Amazon barcode, usually called an FNSKU. Every unit gets a label unique to you and to that listing, so the warehouse tracks your units as yours. The second is the manufacturer barcode, the UPC or EAN already printed on the packaging. Under the old rules, choosing that put your units into a pool with every other seller of the same product who made the same choice. Amazon called this stickerless commingled inventory, and it existed because it was more efficient. Nobody had to apply a label, and the warehouse could ship whichever unit was closest to the customer.

The efficiency was real, and so was the catch. In a commingled pool, the unit that leaves the warehouse under your order number isn't necessarily the one you sent in. Amazon treated the products as interchangeable because the barcode said they were. The customer, and so your account health, does not.

How another seller's unit becomes your problem

Picture a popular kitchen gadget sold by fourteen sellers, nine of them stickerless. Those nine have put their inventory into one shared pool. Eight buy properly from the brand. The ninth buys grey market stock of uncertain origin, or old packaging, or units that were returned, reboxed and sent back in.

A customer orders from you. The fulfilment centre nearest that customer picks from the pool, and the unit that ships is the ninth seller's. It arrives in a faded box, with a broken seal or a manual in the wrong language. The customer does what customers do and reports that the item wasn't new, or that they think it isn't genuine.

The complaint lands on your account, because you were the seller of record on the order. Your account health page shows it, and your Voice of the Customer data gets worse. If enough of these build up on the ASIN, Amazon may ask for invoices proving authenticity. Yours will be genuine and still won't explain the unit the customer received, because that unit was never in your supply chain.

Returns make the pool worse over time. A unit that goes out, comes back, is graded sellable and goes back into stock rejoins the same shared pool. Every restocked return from every participating seller sits in there with your stock. The longer a commingled ASIN had been trading, the more mixed its pool tended to be. Older pooled units can keep shipping for some time after the rule change, so the complaint pattern below is still worth knowing.

The complaint pattern to watch for

Commingling damage has a recognisable signature, and spotting it early can save the listing. Look for these signs together rather than one at a time.

• Condition complaints that don't fit your process: reports of scuffed boxes, missing parts, opened seals or expired dates on a product you know ships factory sealed from a single supplier.
• Reviews describing packaging you don't use. Customers mentioning a different box design, an older logo or a language version you've never stocked is close to conclusive.
• Complaint rates that don't respond to your changes. You improve prep, switch carriers and tighten inspection, and the complaint rate stays where it was, because your handling was never the cause.
• Problems concentrated on your commingled SKUs. If the FNSKU-labelled half of your catalogue is clean and the stickerless half isn't, that's not a coincidence of product category.

Check the barcode setting before you investigate anything else. Sellers often spend weeks auditing their own prep on a problem that a settings page would have explained in thirty seconds. The Voice of the Customer dashboard shows which ASINs are generating negative customer experiences, and your inventory settings show which of them were stickerless. The overlap is your answer.

To find these in Seller Central: Voice of the Customer is under Performance, and the barcode preference sits in Settings, under Fulfillment by Amazon. For each flagged ASIN, compare the complaint dates with when your stickerless units were received. Complaints that cluster while older pooled stock was still shipping point to commingling. Complaints that carry on after only FNSKU-labelled or brand-owner stock remains point back to your own product or prep.

The fix: Amazon barcodes

The fix is simple. In Seller Central, the Fulfillment by Amazon section of your account settings has a barcode preference. Set it to Amazon barcode. From then on, units you send in carry an FNSKU that ties them to you, and they are stored and shipped as yours, outside any pool. For resellers this is now required on inventory shipped from March 31, 2026. For Brand Representatives, a manufacturer barcode no longer means pooling, but the setting is still worth checking so you know how your units are tracked.

Some practical points on the switch:

1. The setting applies to the whole account, with overrides for individual SKUs. You can change the default for everything and still treat particular SKUs differently, which used to be useful for a genuine commodity line where commingling made sense.
2. Someone has to apply the labels. You or your prep partner label units before they ship, or you use Amazon's labelling service where it's offered and pay a per-unit fee. In the US, Amazon has told sellers its prep and item labelling service ended for shipments created on or after January 1, 2026, so US sellers need to label themselves or use a prep provider. Both options cost something. Neither costs as much as a suppressed ASIN.
3. Nothing changes retroactively. Stock already in the network stays where it is, and only new receipts are labelled.
4. Some products were never allowed into the pool. Various categories, including many consumables and topicals, require Amazon barcodes, so parts of your catalogue may already be labelled without you having chosen it.

Brand owners should also look at Transparency, which puts a unique code on every unit and lets Amazon check authenticity at the point of fulfilment. It is more work than a settings change, because the codes go on during manufacturing, but for brands that are repeatedly targeted it deals with the problem at the source.

Cleaning up stock you already sent in

Changing the setting fixes future shipments. Stock already in the pool still ships against your orders, and if the ASIN is already drawing complaints, waiting for it to sell through means accepting more damage in the meantime.

You have two options, and the right one depends on how much harm the ASIN is taking. The passive route is to let existing commingled units sell through while every new shipment arrives labelled, which gradually dilutes the exposure. It costs nothing and it's slow, and it's reasonable when the complaint rate is low and the product isn't central to the brand.

The active route is a removal order. You pull the commingled units back, inspect them, relabel them with FNSKUs and send them in again as clean stock. That costs removal fees, inbound shipping and handling time, and it's the right answer when the ASIN matters and complaints are building. A useful side effect is that you finally see what is actually in the pool, and sellers are often surprised by what comes back, which is an argument for the switch in itself.

Whichever route you choose, do things in the right order. Change the barcode preference first, then deal with the old stock. Doing it the other way round means the replacement shipment can arrive without labels and end up back where you just paid to get out of.

Clean-up checklist

• Confirm the barcode preference reads Amazon barcode (or that you hold the Brand Representative role if you rely on manufacturer barcodes) and take a dated screenshot.
• List every ASIN with stickerless units still in stock, using the inventory reports.
• Rank them by complaint rate and sales value, and decide passive or removal for each.
• For removals, inspect what comes back and record what doesn't match your own stock, with photos.
• Relabel and send back in only units you can confirm are yours.
• Keep supplier invoices for the period ready in case an authenticity review arrives.

Defending a complaint you didn't cause

If the listing is already under pressure you still need to respond, and the response has to deal with what happened rather than protest innocence. A plan of action that just says your stock is genuine won't persuade anyone when the complaint describes a unit that doesn't match your stock.

The stronger approach is to name the root cause honestly and show you've removed it. Your supplier invoices show your sourcing is legitimate. Your explanation identifies commingled fulfilment as the way units outside your control reached your customers. Your corrective action is the barcode change with the date you made it, plus the removal order if you placed one, plus any inspection or Transparency step you've added. That reads as a seller who diagnosed a systems problem, which is what account health reviewers want to see.

Keep the evidence tight. Invoices from an authorised source for the relevant period, with quantities that plausibly cover your sales volume, are worth more than a large pile of documents. Screenshots showing the barcode setting now reads Amazon barcode, and the removal order confirmation, carry weight because they prove a change rather than promise one.

Where a particular complaint is clearly about a unit you didn't supply, say so plainly and briefly, then move on to the fix. Reviewers see a lot of blame-shifting, and you'll be believed when you pair the explanation with a structural change you've already made. Our guide to defending a false counterfeit complaint covers the appeal itself in more detail.

When commingling made sense

It would be wrong to say nobody should ever have used it. Commingling existed because for some inventory it was the right trade. For a genuine commodity where units are functionally identical, unbranded, low value, hard to counterfeit and rarely returned, the labelling saving was real and the downside small. Plenty of sellers ran that way for years without trouble.

The decision always came down to one question: what happens if a customer receives a unit that isn't yours? For a pack of generic cable ties, the answer is a shrug and a refund. For a supplement, a cosmetic, an electrical item, anything for children or any product carrying your own brand, the answer is a complaint that can take the ASIN offline and put your account under review. Those risks aren't comparable, and they shouldn't have had the same setting.

Brand owners in particular should have treated this as close to non-negotiable. You spend money building a brand so the name means something to a customer. Commingling handed quality control of that promise to strangers with no reason to protect it, to save pennies per unit. That trade never made sense, and the sellers who discovered it during a suspension almost always said they had no idea the setting existed. Amazon's 2026 change largely settles the question for new inventory, which is why the remaining risk now sits mostly in older stock.

Frequently asked questions