What Is Fulfilled by Merchant (FBM)?
Fulfilled by Merchant is the opposite of FBA. With Fulfillment by Amazon, you ship inventory to Amazon’s warehouses and they handle everything from storage to delivery. With Fulfilled by Merchant, you keep inventory in your own facility (or a 3PL) and ship directly to buyers when orders come in. Amazon still processes the payment and provides the order details, but the physical fulfillment is entirely your responsibility.
The biggest operational difference with Fulfilled by Merchant is speed. FBA orders get Prime two-day (or same-day) delivery automatically. Fulfilled by Merchant orders default to standard shipping windows of 3 to 5 business days unless you qualify for Seller Fulfilled Prime, which requires near-perfect delivery metrics. This speed gap directly affects conversion rates: listings with the Prime badge convert 2x to 3x higher than non-Prime listings in the same search results.
Fulfilled by Merchant sellers must maintain a Valid Tracking Rate above 95%, Late Shipment Rate below 4%, and respond to customer messages within 24 hours. FBA absorbs all of these requirements. The tradeoff is control: FBM gives you full visibility into your shipping costs, packaging quality, and customer experience. FBM also sidesteps restock limits and IPI score pressures entirely.
FBM fee structure for FBA sellers
Pick & pack labor (or 3PL fee)
+ Packaging materials
+ Outbound shipping (carrier rate)
+ Storage cost per unit per month
+ Return processing (if applicable)
FBA cost per unit =
FBA fulfillment fee (covers pick, pack, ship)
+ Monthly storage fee
+ Inbound shipping to Amazon FC
+ Inbound placement fee (if applicable)
Example: FBM margin analysis on a $32 product
A seller running $2.2M annually with 40 SKUs considers switching one product to FBM: a 1.8 lb supplement priced at $32, selling 35 units per day. Under FBA, the fulfillment fee is $4.75 per unit (standard size, 1 lb+). Monthly storage at $0.78/cubic foot allocates to roughly $0.18 per unit. Total FBA cost: $4.93 per unit.
Under FBM with a 3PL, the breakdown is: $1.90 pick and pack + $0.45 packaging + $4.80 USPS Priority Mail (negotiated rate) + $0.12 storage = $7.27 per unit. FBA saves $2.34 per unit, or $2,989 per month at 35 units/day. On top of that, removing the Prime badge would likely drop conversion by 25% to 40%, costing an additional $4,000 to $6,400 monthly in lost sales.
FBM only makes sense for this SKU if FBA storage limits block the seller from sending enough inventory, or if the product is a slow mover racking up IPI-damaging excess inventory fees in FBA.
Common mistakes
- Switching to FBM without running the full cost comparison. Sellers often compare only the FBA fee against their shipping cost, ignoring the conversion rate drop from losing Prime. A 30% conversion decrease on a $32 product selling 35 units/day costs $10,080/month in lost revenue.
- Running FBM and FBA on the same ASIN without a repricing strategy. If your FBM offer sits at the same price as competing FBA offers, you will rarely win the Buy Box. FBM offers typically need to be priced 3% to 8% lower to compete.
- Underestimating customer service load. FBM sellers handle all A-to-Z claims, return processing, and buyer messages directly. A seller doing 1,000 FBM orders/month should budget 15 to 20 hours/month of customer service labor.