How to Sync eBay and Amazon Inventory Automatically (UK 2026)

Why they won't sync themselves

eBay and Amazon are direct competitors. Neither has any interest in telling the other what you've sold, and there's no native connection between them. Each simply tracks its own listing's quantity, in isolation.

So when a unit sells on Amazon, your eBay listing has no idea — it still shows the item available, ready to sell stock you no longer have. Bridging that gap needs a third party: a tool that connects to both via their seller APIs, holds the real stock figure, and updates each. That's the whole job.

The prerequisite: consistent SKUs

Before any sync can work, software needs to know that a listing on eBay and a listing on Amazon are the same product. It does that by matching SKU — your internal stock code.

If "TSHIRT-BLK-M" is the SKU on both your eBay and Amazon listings, a sync tool knows they draw from one stock pool of that item. If your SKUs are inconsistent — different codes on each channel, or missing entirely — no tool can match reliably, and sync fails before it starts. So the real first step isn't choosing software, it's getting a clean, consistent SKU onto every listing across both channels. Our SKU guide covers building a system that survives multi-channel selling.

The manual method (and where it breaks)

At tiny volume, you can sync by hand:

1. A unit sells on Amazon.
2. You log into eBay and reduce that listing's quantity by one.
3. Repeat, in both directions, for every sale.

This genuinely works — until it doesn't. The failure point is the gap between the sale and your update. Sell your last unit on Amazon at 2pm, and until you manually zero the eBay listing, an eBay buyer can buy it too. On a quiet week you might get away with it; during a busy spell, or overnight, or the moment you're away from your desk, you oversell. The manual method doesn't scale because oversells scale faster than your ability to update by hand.

Automatic real-time syncing — how it works

The real solution puts one central stock count in charge:

1. Your products live once in a central catalogue, each with its SKU and a true stock quantity.
2. The tool connects to eBay and Amazon via their seller APIs and matches your listings by SKU.
3. A sale on either channel immediately reduces the central count.
4. The tool pushes the new quantity to the other channel within seconds.

The word that matters is real-time. Some tools sync on a schedule — every 15 minutes, every hour — and that interval is exactly the window an oversell slips through. For two high-traffic channels like eBay and Amazon, insist on real-time updates, not batches. Our overselling guide covers why sync frequency is the whole game.

It also works in your favour beyond safety: with one stock pool, you can list your full quantity on both channels rather than splitting it (50 on eBay, 50 on Amazon), because whichever sells draws from the same 100. You get maximum exposure on both without the risk that used to force sellers to hold stock back.

The FBA wrinkle

If some of your Amazon stock is in FBA(Fulfilled by Amazon), there's a nuance: that stock physically sits in Amazon's warehouses and Amazon controls its quantity. You generally can't sync FBA stock to eBay the same way, because you can't ship an eBay order from Amazon's FBA inventory. Sellers usually keep a separate pool of self-fulfilled stock for eBay, and sync that. Our FBA inventory guide covers managing the two pools.

Setting it up with Salync

Salync is built for exactly this: connect eBay and Amazon (plus Shopify and the UK marketplaces), it matches your listings by SKU into one catalogue, and every sale on any channel updates the others in real time. Import your existing listings, fix any SKU gaps it flags, and the overselling problem is solved from then on — no manual quantity edits, no scheduled-batch gap. Free for up to 50 SKUs.