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Centralizing marketplaces means receiving every order in a single queue and keeping one stock figure, pushed back to each channel. An off-the-shelf aggregator is often enough; a custom tool, at $6,800 to $22,400 (€6,000–€20,000)excl. VAT, makes sense when your stock, fulfillment or invoicing rules go beyond the standard.
Selling on your own store, on Amazon and on other marketplaces multiplies sales, but also screens. Each channel has its own interface, statuses and stock. Without a central tool, the team jumps from tab to tab and the risk of selling a product that is already gone goes up. Here is how to centralize orders and stock, and when to do it with custom software.
The real problem: one stock, several storefronts
A marketplace is just one more storefront. Your stock, however, is unique and sits in your warehouse. The difficulties always come from the same places:
- overselling: one product sold on two channels a few minutes apart;
- statuses: shipping on one channel, forgetting to confirm shipment on the other, and watching your seller rating drop;
- invoicing: each channel has its own fees and rules, which makes margin calculations harder;
- picking: three order lists to merge every morning.
A central tool reverses the logic: all orders land in a single queue, stock is kept in one place, then pushed to each channel.
How the tool connects to marketplaces
Major marketplaces offer APIs to their sellers. Amazon, for example, provides the Selling Partner API, which gives access to data on orders, shipments, payments and inventory (documentation checked October 2026). Other marketplaces have their own interfaces, with different formats and rules that change over time. The channel-by-channel detail is covered in connecting marketplaces.
Technically, the central tool:
- pulls new orders from each channel at short intervals;
- converts them into a common format;
- reserves stock immediately;
- drives picking and shipping;
- sends the status and tracking number back to the original channel;
- recalculates and publishes available stock on every channel.
Each connector is isolated: if a marketplace changes its API, we update one module without touching the rest.
Off-the-shelf aggregator or custom tool
Feed aggregators and multichannel management software exist on the market. For many companies, they are the right answer. Here is how I tell the difference.
| Criterion | Off-the-shelf aggregator | Custom tool |
|---|---|---|
| Getting started | Fast, ready-made connectors | 1 to 3 months |
| Cost | Subscription, often tied to volume or number of channels | Upfront investment, then maintenance |
| Stock rules | Standard | Yours: buffer per channel, batches, warehouses |
| Picking | Often basic or handled by another tool | Built around the way you pick |
| Margin by channel | Depends on the tool | Calculated with your real costs |
| Connection to your systems | Connectors available, or not | Built for your ERP or accounting |
Custom software wins when you have several warehouses, products sold in bundles or kits, a specific picking process, or when you pay for an aggregator, a picking tool and a margin spreadsheet all at once.
Budget and timelines
These ranges exclude VAT, cover a first version running in production and follow my public price list.
| Scope | Example | Indicative budget | Timeline |
|---|---|---|---|
| Add-on module | Picking or margin by channel, plugged into your aggregator | $6,800 to $13,500 (€6,000–€12,000)excl. VAT | 1 to 2 months |
| Focused central tool | Unified orders and stock for 2 or 3 channels | $11,200 to $22,400 (€10,000–€20,000)excl. VAT | 2 to 3 months |
| Complete central tool | Several channels, warehouses, purchasing, ERP or accounting connection | $16,800 to $39,200 (€15,000–€35,000)excl. VAT | 3 to 5 months |
In my estimator, each connection to an external tool counts for about $2,300 (€2,000)excl. VAT, a dashboard $1,700 (€1,500)excl. VAT and data migration $900 (€800)excl. VAT. The estimator gives you a range in one minute.
When it is not the right choice
- One or two channels, a small catalog. Seller dashboards and a simple aggregator are enough.
- An aggregator that works well. Do not replace it: extend it if one specific point is blocking you.
- A catalog still being built. If your product data is not stable yet, sort that out first.
- One marketplace that accounts for most of your sales and offers its own fulfillment. In that case, the marketplace’s tools may be enough, and custom software adds little value.
Where to start
- A 30-minute call (free): your channels, your volumes, your current tools.
- Scoping (1 to 2 weeks): order flows, stock rules, choice of the first channels, fixed quote.
- Clickable mockups of the order queue and stock screens.
- Development in batches: one channel first, tested on real orders, then the next ones.
- Go-live, training, three months of included support.
If your stock is already managed in an in-house tool or a spreadsheet, the inventory management app page shows what the stock part can include.
Frequently asked questions
How often should stock be synchronized?
As often as possible, ideally on every movement. Each marketplace limits how often you can call its API, so we combine immediate updates for sensitive products with regular syncs for the rest.
What about products sold on two channels at the same time?
We keep a safety buffer per channel and reserve stock as soon as the order arrives, before picking. Zero risk does not exist, but a good reservation rule makes it rare.
Can the tool manage product listings on each marketplace?
Yes, but it is a separate project. Each marketplace has its own categories and required attributes. I often advise starting with orders and stock, then adding listing management if the volume justifies it.
Can we keep our current aggregator and just add a module?
Yes. If the aggregator handles the feeds well, a custom tool can plug into it for picking, margin by channel or invoicing. It is often the cheapest option.