What a 3PL actually does
Third-party logistics (3PL) is an umbrella term for outsourcing some combination of warehousing, order fulfillment, and transportation to a specialist provider instead of running it in-house. The scope varies a lot by provider—some only handle storage and shipping, others manage full pick-pack-ship fulfillment integrated with your storefront, and some also handle inbound freight and customs.
The main types of 3PL provider
Providers tend to specialize, and picking the wrong type for your needs is a common source of a bad 3PL fit.
- Warehousing/storage 3PL: provides space and basic inventory handling, without necessarily managing fulfillment
- Fulfillment 3PL: picks, packs, and ships orders on your behalf, often integrated directly with an ecommerce platform
- Transportation/freight 3PL: manages shipping and freight without warehousing—moving goods, not storing them
- Freight forwarder: coordinates international shipping and customs, often as one piece of a larger logistics chain
- Lead logistics provider (4PL): manages and coordinates multiple other logistics providers on your behalf, one level removed from the physical operations
Where 3PL savings actually come from
The honest version of "3PLs save money" is usually one of three specific things: shared warehouse space and labor spread across many clients (cheaper than leasing and staffing your own facility at low volume), negotiated freight rates the 3PL gets from shipping at scale across all its clients, and not carrying the fixed cost of a warehouse team through slow seasons.
None of those savings are automatic—they depend on your volume being a good fit for the provider's model, and on the 3PL's fees (storage, pick, pack, and per-order charges) actually coming in below what running it yourself would cost at your scale.
What you give up, and how to weigh it
The main trade-off is inventory visibility. Once stock physically sits in a 3PL's warehouse, you see it through their reporting rather than direct observation—and 3PL inventory reports can lag, especially around receiving discrepancies, damage, or misplaced units. Businesses that skip keeping any of their own record for what they sent the 3PL have no way to catch a mismatch until it shows up as an unexplained stockout or overselling event.
The fix is not avoiding 3PLs—it is not treating their reporting as the only source of truth. Keep your own record of what you sent to the 3PL (shipment contents, dates, quantities) so you have something concrete to reconcile against their received and on-hand figures, the same way FBA sellers reconcile prep-warehouse records against Amazon's inbound reports.
A short checklist for choosing a 3PL
Match provider type to what you actually need (storage vs. full fulfillment vs. freight), confirm their fee structure against your real order volume and average order size, and ask directly how inventory discrepancies get reported and resolved—a vague answer there is a warning sign, since discrepancy handling is where most 3PL relationships actually break down.
- Confirm which type of 3PL you actually need before comparing quotes
- Model their fee structure against your real volume and average order size, not a sales estimate
- Ask specifically how inventory discrepancies are reported and resolved
- Check integration options for keeping your own stock records in sync with theirs
If you are the 3PL: keeping client stock separate
Seen from the provider's side, the core record-keeping problem is ownership. A 3PL stores stock for several clients in one building, often in the same racking, so every unit needs an owner as well as a location. Counts, picks, receipts and storage invoices all have to be correct per client, and the error clients notice first is their stock showing up on someone else's line.
Small providers often start with one spreadsheet or one software account per client. That works until the same team has to receive, move and ship for every client in a shared warehouse. Inventory software that records the client on each product keeps one set of locations and one stock history, while still reporting stock, receipts and shipments per client. For how that works in StockFlow, see the 3PL inventory management software page.
- Record an owner (client) on every product, not only a location
- Keep quantities per product per bin so clients can share shelves safely
- Report stock on hand, locations used, receipts and shipments per client
- Use those per-client figures as the input for storage and handling invoices
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