📋 Overview
Prep and labeling problems are expensive in a quiet way: the units still sell, but each inbound shipment carries charges you never planned for, plus delayed receipt while a fulfillment center works out what to do with non-compliant cartons. Amazon has moved away from routinely fixing prep and labeling on your behalf at the fulfillment center, which makes “we’ll let Amazon handle it” a weaker plan than it used to be.
This article walks through how FBA prep requirements are assigned per SKU, how to build a repeatable prep and labeling process before inventory leaves your supplier or 3PL, and how to audit inbound charges so you catch problems after one shipment instead of ten.
🎯 Who This Is For
🌱 Beginner sellers
- You’re sending your first few FBA shipments and aren’t sure what an FNSKU is or when you need one.
- You sell apparel, plush, liquids, or glass and keep seeing prep warnings in the inbound workflow.
- You want to know why your FBA fees don’t match what you estimated.
🚀 Advanced sellers
- You’re moving prep upstream to a supplier or prep center and need a written spec they can follow.
- You want to reconcile inbound charges line by line and dispute the ones that are wrong.
- You’re scaling SKU count and need prep decisions made once, at listing setup, rather than repeatedly at ship time.
🔑 Key Concepts You Need to Know
🏷️ FNSKU vs. manufacturer barcode
An FNSKU is the Amazon-generated barcode that ties a physical unit to your specific seller account. If you use it, every unit needs that label applied and any other scannable barcode on the packaging covered. The alternative is a manufacturer barcode (UPC/EAN), which puts your units into commingled inventory alongside other sellers’ identical units. Most private-label sellers use FNSKU labels.
🧰 Prep guidance
Amazon assigns prep requirements at the product level based on category and physical characteristics — polybagging, bubble wrap, opaque bagging, taping, sold-as-set labeling, and so on. You see this guidance per SKU inside the Send to Amazon inbound workflow. Guidance can change when a listing’s category or attributes change, so it is worth re-reading, not memorizing.
⚠️ Non-compliance charges
Amazon has moved away from selling per-unit prep and labeling as a service performed on arrival. The practical effect is that inventory is expected to arrive fully prepped and labeled, and shipments that don’t comply can trigger fees, delayed receipt, or refusal. Because fee names and amounts change on Amazon’s own schedule, check the current charge names and rates in your account’s FBA fee schedule rather than relying on figures you saw last year.
📦 Box content information
This is the declaration of which SKUs, in what quantity, sit inside each carton. Providing it accurately — by upload or by 2D barcode on the carton — is what lets a fulfillment center receive your shipment without manual handling. Missing or inaccurate box content data is one of the most common sources of unexpected inbound charges.
🛠️ Step-by-Step Guide
1️⃣ Read prep guidance before you buy the inventory
Open the Send to Amazon workflow from Manage Inventory and start a draft shipment with the SKUs you plan to reorder. Read the prep and labeling requirements listed against each SKU before you place the purchase order, not after the pallets arrive.
Good result: you know, per SKU, whether it needs a polybag, bubble wrap, a set label, or nothing beyond an FNSKU — and you know that before you’ve paid a supplier.
2️⃣ Decide your barcode strategy per SKU
Choose FNSKU labeling or manufacturer barcodes deliberately. FNSKU costs you a label and an application step but keeps your units traceable to your account. Commingling removes the labeling step but pools your units with other sellers’ stock of the same product.
If you choose FNSKU, the label must be scannable, flat, and unobstructed, and every other barcode on the outer packaging must be fully covered.
3️⃣ Write a one-page prep spec per SKU
Turn the guidance into an instruction sheet your supplier or prep partner can follow without asking questions: bag type and size, label placement, warning text, taping, and what the finished unit should look like. Include a photo of a correctly prepped unit.
- Poly bags used for FBA must be at least 1.5 mil thick.
- A poly bag with an opening of 5 inches or more requires a suffocation warning that stays legible after sealing.
- Units sold as a set need a “sold as set, do not separate” instruction visible on the outer packaging.
- Expiration-dated goods carry their own labeling and remaining-shelf-life rules — confirm the current requirements in Amazon’s expiration-dated inventory policy before shipping.
💡 Pro Tip: Send the spec sheet to your supplier as part of the purchase order, not as a separate email. Prep completed at the factory almost always costs less per unit than prep completed after the goods land.
4️⃣ Pack cartons to Amazon’s carton limits
Standard-size shipping cartons may be up to 36 inches long, with width and height capped at 25 inches and weight capped at 50 lb. A carton may exceed these only when a single unit inside genuinely exceeds them.
Cartons over 50 lb need a team lift label; very heavy cartons need a mechanical lift label. Confirm the current weight thresholds for those labels in Amazon’s packing and shipping requirements before you print them.
Good result: no carton on the pallet is over-dimension or over-weight, and every one is labeled with its own unique shipment label.
5️⃣ Submit accurate box content information
Complete box contents in the inbound workflow before the shipment leaves. Match the physical carton to the declared contents exactly — including quantity. If your prep partner repacks, get their final carton manifest before you submit, not after.
6️⃣ Reconcile every shipment after receipt
Once the shipment closes, compare units shipped against units received in the shipment’s reconciliation view, and cross-check movement in the Inventory Ledger Report under Reports > Fulfillment > Inventory Ledger. Discrepancies have a filing window, so make reconciliation a scheduled task rather than an occasional one.
7️⃣ Audit the charges against your estimate
Pull your fee detail from the payments transaction reports and compare the per-unit economics against the Fee Preview estimate for the same ASINs. Any inbound charge that isn’t fulfillment, referral, or storage deserves a look — that’s usually where prep, labeling, or box-content problems show up.
💡 Pro Tip: Tag charges by shipment ID in your own spreadsheet. One noisy shipment tells you which supplier, prep partner, or SKU broke the process, which a monthly fee total never will.
8️⃣ Update the spec and close the loop
Every non-compliance charge should end with a change to the spec sheet, the packing instruction, or the partner relationship. If nothing changes, the same charge appears on the next shipment.
💼 Real-World Examples
🧸 A newer seller with 6 plush SKUs
Problem: Units shipped loose in master cartons. Plush and textile products generally require polybagging, and the shipments arrived without bags or suffocation warnings, generating charges on every inbound and slowing receipt.
Action: The seller added a bagging line to the supplier’s purchase order with bag dimensions, mil thickness, and the warning text, and requested FNSKU labels applied at the factory with a photo of correct placement.
Result: Later shipments received without prep-related charges, and receive times became more predictable — a directional improvement visible across the following two or three inbound cycles.
🏭 A mid-size seller with 40 ASINs across two prep partners
Problem: Inbound charges appeared inconsistently, and nobody could say which partner caused them because fees were only reviewed as a monthly total.
Action: The seller began tagging every charge by shipment ID and partner in a shared sheet, then reconciled each closed shipment against the Inventory Ledger Report. The pattern pointed to one partner repacking cartons after box contents had been submitted.
Result: After moving box-content submission to happen only on the partner’s final manifest, discrepancy cases dropped and the unexplained charge line largely disappeared over subsequent shipments.
🚧 Common Mistakes to Avoid
❌ Assuming Amazon will fix prep at the fulfillment center
Sellers do this because it was once a routine paid service. Treat the fulfillment center as a receiving dock, not a prep station: anything that isn’t done before the carton is sealed is a risk, not a line item you can budget for.
⚠️ Leaving the manufacturer barcode exposed under an FNSKU label
A partially covered UPC can be scanned instead of your FNSKU, which causes misidentified receipts and inventory that doesn’t land where you expect. Cover the original barcode completely — with an opaque label or a sticker large enough that no digits or bars show.
🚫 Submitting box contents from the packing plan instead of the actual cartons
Plans change on the floor. When declared contents and physical contents disagree, receipt slows and charges follow. Confirm the final manifest with whoever sealed the boxes before you submit.
❌ Never reconciling closed shipments
Sellers skip reconciliation because the units eventually show up. Discrepancy claims have filing windows, and a shipment you never checked is a shipment you can no longer dispute. Put it on a weekly calendar block.
📈 Expected Results
Watch these, per shipment rather than per month:
- Non-fulfillment inbound charges per shipment — the clearest signal that prep or box contents are wrong. Should trend toward zero once specs are enforced upstream.
- Units shipped vs. units received — a shrinking gap means your carton manifests and box content data agree.
- Time from carrier delivery to fully received — compliant, accurately declared shipments generally clear receiving faster than ones requiring manual handling.
Expect to see the effect after roughly two to three inbound cycles, since each shipment is a single data point and charges post after receipt. The durable benefit is operational: prep decisions get made once, at SKU setup, and stop consuming attention every time you restock.
❓ FAQs
🏷️ Can my supplier apply FNSKU labels for me?
Yes. You generate the labels from your inventory tools and send the print files to the supplier or prep partner. Ask for photos of a labeled unit from the first production run before the full order is packed.
🔍 How do I know which prep a specific SKU needs?
Start a draft shipment in Send to Amazon from Manage Inventory and read the prep and labeling requirements shown against that SKU. Cross-check against Amazon’s packaging and prep requirements pages for your category, since guidance can update.
💵 I was charged something I don’t recognize on an inbound shipment. What now?
Identify the charge in your payments transaction detail, tie it to a shipment ID, then open a case with the shipment ID, the charge name, and photos of how the units were prepped. Photographic evidence taken at packing time is what makes these cases resolvable.
📏 Can a carton ever exceed the standard-size limits?
Only when a single unit inside genuinely exceeds them. You cannot combine several small items into an oversized carton to save on freight — that carton will be treated as non-compliant.
🔄 Should I use FNSKU or commingled inventory?
FNSKU for anything branded, anything with quality or authenticity exposure, and anything where you want your specific units traced to you. Commingling mainly makes sense for generic, low-differentiation goods where the labeling step outweighs the traceability benefit.