Every prep mistake starts as a word someone didn’t quite understand. A unit gets rejected because nobody was sure what an FNSKU actually was, or a shipment eats a defect fee because “poly-bag required” sounded optional. This is the prep vocabulary that decides whether your inventory gets received or sent back — thirty terms, defined the way one seller would explain them to another, not the way a help-doc would.
They’re grouped so you can find what you need fast: identifiers and labels, then the physical prep work, then logistics and storage, then the fees, rules, and players. Where a term links somewhere, that’s because there’s more worth saying about it than a glossary line allows.
Identifiers and labels
The codes Amazon uses to tell one seller’s units apart from another’s. Get these wrong and the warehouse can’t tell whose inventory it’s holding.
FNSKU (Fulfillment Network Stock Keeping Unit)
The ten-character code Amazon assigns to a specific product from a specific seller. Think of it as the unit’s passport inside Amazon’s warehouses: it ties that physical item to your account and nobody else’s. Two sellers offering the identical product still get different FNSKUs. The label carrying this code has to be scannable and has to sit over any existing manufacturer barcode, or the warehouse reads the wrong product. (See FNSKU labeling.)
FNSKU labeling
The act of printing and applying FNSKU labels to every unit before it reaches Amazon. Sounds trivial; isn’t, at volume. The label has to be machine-readable, positioned where the scanner expects it (usually the lower-right of the front face), and placed so it doesn’t wrinkle on soft packaging or distort over a curve. A label Amazon can’t scan counts as no label at all — and now triggers a fee. Since Amazon stopped doing this in 2026, it’s the prep task most sellers outsource first. We price it from $0.25 a unit on our Launch Program; the pricing page has the full breakdown.
UPC (Universal Product Code)
The standard retail barcode printed by the manufacturer, shared across every seller of that product. It identifies the product, not your units. On Amazon it’s used to create a listing, but it can’t keep your inventory separate from another seller’s — that’s the FNSKU’s job.
EAN (European Article Number)
The international cousin of the UPC, thirteen digits instead of twelve, common on products sourced outside North America. Functionally interchangeable with a UPC for listing purposes. Same limitation: identifies the product, not your specific units.
ASIN (Amazon Standard Identification Number)
Amazon’s ten-character ID for a listing — the product detail page customers see. Every product on Amazon has one. It’s not printed on your units and has nothing to do with prep directly, but you’ll see it constantly, so it’s worth knowing it refers to the page, not the physical item.
SKU (Stock Keeping Unit)
Your own internal code for a product — whatever naming system you use to track inventory in your own records. Amazon stores it but doesn’t enforce its format. Don’t confuse it with the FNSKU: the SKU is yours, the FNSKU is Amazon’s.
Commingling
When Amazon pools identical units from multiple sellers into shared inventory, ignoring whose is whose, because the products carry a manufacturer barcode instead of seller-specific FNSKUs. It saves a labeling step — and means a customer might receive a unit a different seller sourced, including a counterfeit, with the complaint landing on you. Most sellers who care about account health label every unit with an FNSKU to stay out of the commingled pool. Amazon adjusted its commingling rules in March 2026, but the safer default for resellers hasn’t changed: label your own units.
Stickerless (commingled inventory)
The flip side of labeling: enrolling a product without FNSKU labels so it joins the commingled pool. Tempting because it skips a step. Risky for the reasons above. The word shows up in Seller Central as an option — treat it as one you’re declining on purpose.
Physical prep
The hands-on work of getting a unit compliant. Amazon spells out the requirements; since 2026 it no longer performs any of them for you.
Poly-bagging
Sealing a unit in a polyethylene bag. Required for apparel, textiles, and soft goods, and anything where loose units could get damaged or contaminated. Bags five inches or larger on a side must carry the printed suffocation warning, or the bag itself becomes a defect. Cheap to do right, expensive to skip.
Bubble wrapping
Wrapping fragile items so they survive Amazon’s handling — glass, ceramics, electronics, anything that rattles. The standard isn’t “looks protected,” it’s “survives a drop and a conveyor belt.”
Protective packaging
The broader category beyond bubble wrap: corner protectors, dunnage, over-boxing, void fill. Whatever it takes to get a fragile or oddly-shaped unit through Amazon’s network intact. Under-packing shows up later as damage claims; over-packing wastes money on dimensional weight.
Bundling and kitting
Combining multiple units into one sellable set — a three-pack, a gift set, a starter kit sold under a single listing. The work is doing it so the bundle arrives as one unit and can’t be pulled apart by warehouse staff. Bundles need a clear “sold as a set” or “do not separate” label. Amazon won’t assemble them, and a bundle that arrives as loose units gets treated as loose units, usually with a fee attached.
Expiration and lot labeling
For consumables, supplements, and anything dated: the expiration date has to be printed in a specific format, in a specific place, readable by the warehouse. Get it wrong and the goods can be refused at receiving — and dated inventory you can’t get received is inventory you watch expire.
Hazmat prep
Compliance work for anything Amazon classifies as hazardous: aerosols, lithium batteries, flammables, certain liquids. Its own documentation and labeling rules, and the category where a mistake is most expensive, because the penalty can be a shipment refused outright. If you’re not certain whether your product is hazmat, that uncertainty is worth a conversation before you ship.
Suffocation warning
The printed warning required on any poly-bag five inches or larger on a side. Small detail, real consequence: a bag missing it is a compliance defect even if the bag is otherwise perfect. The kind of thing in-house teams forget and prep centers catch by reflex.
Sticker removal / repackaging
Pulling off retailer stickers, price tags, or old barcodes and repacking a unit so it arrives looking like new inventory rather than a returned item. Common for retail-arbitrage and wholesale sellers. Skipped, it shows up as a customer complaint about “used” goods.
Inspection / quality check
The visual pass before anything ships: right product, right quantity, no defects, working parts, correct SKU. The cheapest insurance in the whole prep chain, because catching a bad unit in the warehouse costs cents — catching it after a customer does costs a return, a refund, and sometimes a review.
Logistics and storage
How inventory moves into the prep center, sits, and leaves — and the words on the invoice for each step.
Receiving
The intake step: a prep center accepts your inbound shipment, counts it against what you said was coming, and logs any discrepancy or damage. Usually its own line item — a receiving fee — separate from per-unit prep. The count that happens here is your first proof of what actually arrived.
Forwarding
The outbound step: after prep, the center ships your units onward to Amazon or Walmart. “Forwarding” or “outbound shipping” on an invoice. The shipping itself should be a pass-through at carrier rates (see pass-through shipping) — the service is the work of creating the shipment, labeling cartons, and dispatching.
Box content labels
The information Amazon requires about what’s inside each carton — which SKUs, how many of each. Provided as a 2D barcode or an uploaded manifest so the fulfillment center can check a box in without opening and counting it. Missing or wrong box content data slows receiving and can trigger a manual-processing fee.
Pallet / LTL shipping
LTL (less-than-truckload) is how palletized inventory moves when you have more than parcel carriers handle well but less than a full truck. Relevant once your volume outgrows boxes. A prep center that ships pallets to Amazon can consolidate your units onto fewer, cheaper freight lanes than parcel.
Storage fees
What you pay to hold inventory at the prep center between receiving and forwarding. Short dwell time is cheap; inventory that sits for weeks isn’t. Worth watching, because storage is where a “cheap” prep quote quietly gets expensive if turnaround is slow.
Turnaround time
The clock from received to shipped. The industry standard is 24–48 hours. Slower than 72 hours becomes a problem in peak season; faster than 24 is either real automation or a corner cut. It’s one of the few prep metrics worth asking about directly before you commit.
Pass-through shipping
Shipping billed at the actual carrier rate with no markup. The honest way to invoice freight. If a quote lists “shipping fees” without showing the underlying UPS/FedEx/LTL rate, the gap between the two is margin you’re paying. Ask for the breakdown.
Fees, rules, and the players
The vocabulary of what prep costs, who does it, and what happens when it’s wrong.
Inbound defect fee
The fee Amazon introduced in January 2026 — $0.60 per unit — for anything that arrives with a prep or labeling problem it used to fix for you. Missing FNSKU, missing poly-bag, unbundled bundle, unlabeled hazmat: each defective unit is charged, per unit, not per shipment. Five hundred mislabeled units is $300 on top of your regular fees, which for a thin-margin product can erase the profit on the whole shipment.
Before 2026, a prep mistake cost you a small per-unit correction fee and Amazon fixed it. Now the unit gets charged $0.60 and bounced back unprepped — you pay the fee and still have to fix it, while the inventory sits unsellable. The cost of a mistake didn’t go up a little. It roughly doubled and added a delay.
Prep fee vs. receiving fee
Two different line items that get confused. The prep fee is per unit, for the work done to each item (labeling, bagging). The receiving fee is for accepting and counting an inbound shipment, often charged per box or per shipment. A quote that shows only one of the two isn’t necessarily cheaper — it may just be hiding the other.
Prep center (third-party prep, 3PL)
A warehouse that receives your inventory, performs the prep — labeling, bagging, bundling, whatever the product needs — and forwards it to Amazon or Walmart. Pricing is per unit for the prep, with separate line items for receiving, storage, and shipping. It’s the path most sellers in the hundreds-to-thousands-of-units-a-month range take, because it buys compliance expertise without making you build a prep operation yourself. What separates a good one from a bad one is on our list of what to look for in a prep partner.
3PL (third-party logistics)
The broader term a prep center falls under: any outside company that handles warehousing, fulfillment, or logistics on your behalf. All prep centers are 3PLs; not all 3PLs do Amazon prep. When a provider calls itself a 3PL, check that FBA prep is a real service and not a bolt-on.
FBA (Fulfillment by Amazon)
You send inventory to Amazon; Amazon stores it, picks it, ships it, handles returns. Prime-eligible by default. Prep happens before it reaches Amazon — which, since 2026, means before it reaches Amazon, someone other than Amazon has to do it.
FBM (Fulfillment by Merchant)
You store and ship orders yourself. Different model, different logistics. A prep center that understands both can support you whichever way you sell, or both at once.
WFS (Walmart Fulfillment Services)
Walmart’s answer to FBA: Walmart warehouses your inventory and fulfills your Walmart Marketplace orders. Prep rules resemble Amazon’s but aren’t identical — different label specs, different fulfillment centers (Pedricktown, NJ is the big one). A prep partner who treats WFS as a real service, not an afterthought, saves you running two separate workflows.
Fulfillment center (FC)
Amazon’s warehouse — where your prepped inventory lands, gets stored, and ships from when an order comes in. Your prep has to satisfy the FC’s receiving requirements, because the FC is where defects get caught and fees get charged.
Seller Central
Amazon’s dashboard for third-party sellers — where you create shipments, see prep requirements, manage listings, and watch your account health. The prep rules that matter live here, under Packaging and Prep Requirements. When a prep instruction is ambiguous, this is the source of truth.
Where this leaves you
The through-line in all of it: since January 2026, every requirement above is yours to meet, and every miss has a price. The terms aren’t trivia — each one is a place a shipment can go wrong.
South Way Prep handles the whole list — FNSKU labeling from $0.25 a unit, poly-bagging, bundling, hazmat, receiving, forwarding, both Amazon FBA and Walmart WFS — from a warehouse in Pompano Beach, Florida. Per-unit pricing published in plain numbers, no quote form required to see a rate.