Multichannel Inventory Management: How Do You Set Up Shared Stock?

Multichannel inventory management is the work of keeping the quantity shown on each channel in line with the actual stock in your warehouse while you sell the same product on Trendyol, Hepsiburada, n11, Amazon, Temu and your own website at the same time. The safest method is to keep stock in a single central record (shared stock), link each channel's listing to that record by barcode and SKU, and push the updated count to every channel after each sale, cancellation or return. In this guide, we explain how to set up shared stock step by step, where mistakes happen most often, and what you should check regularly after setup.

Why does inventory management get harder when you sell on multiple channels?

Each marketplace keeps its own stock count in its own panel. As you update these counts one by one, short- or long-lived discrepancies appear between channels. Typical causes include:

• Manual updates: Stock is changed in one panel, and the others are forgotten.
• Delays: Until an order on one channel is reflected on the others, the same product can also be sold on another channel.
• Mapping errors: A sale of one size is deducted from another size's stock.
• Unprocessed cancellations and returns: A returned product isn't added back to stock, or a damaged product mistakenly ends up in sellable stock.
• Warehouse movements: Shrinkage, damage and count discrepancies aren't recorded.

The cost of overselling

Overselling means selling a product you don't have. Most of the time, you end up having to cancel the order. Marketplaces track seller-caused cancellations in their performance metrics; as cancellations rise, your store rating, listing position and account status can be affected. Thresholds and sanctions differ on each platform, so follow the current rules in your seller panel.

If you choose to source the product afterward and ship it, also factor in the legal limit in Türkiye: in a distance sale (mesafeli satış), the seller must ship the goods within the promised time and, in any case, within 30 days at the latest. Marketplaces' deadlines for handing orders to the carrier are much shorter than that.

We summarized the basic logic of synchronization in our article what is stock synchronization; this guide focuses on setup and day-to-day operations.

The shared stock model: one center, many storefronts

In the shared stock (master stock) model, the single source of truth for stock sits at the center; marketplace panels are storefronts where that record is displayed. Channels don't set the stock count themselves; they take it from the center.

With shared stock, the question "How many units of this product do we have?" has only one answer. When a sale happens on one channel, the quantity is deducted at the center and the new count goes out to every channel. Whichever channel the last unit sells on, it also shows as out of stock on the other channels.

Step 1: Organize your product identifiers (barcode and SKU mapping)

Shared stock works by linking each channel's listing to the correct record at the center. What creates that link is product identifiers. Marketplaces mostly recognize a product by its barcode; the code in your internal system is the SKU.

The three identifier fields in Trendyol's product creation documentation are a good starting point:

Follow these rules when mapping:

• The stock unit is the variant. "Black T-shirt" isn't a stock record; "black T-shirt, size M" is. On Trendyol, slicer attributes such as color create separate product cards, while varianter attributes such as size create options on the same card; in both cases, each variant has its own stock.
• One barcode per variant. Using the same barcode on two variants causes a sale of one size to be deducted from the other size's stock.
• The same identifier on every channel. A variant should be defined with the same barcode and the same SKU on Trendyol, Hepsiburada and Amazon. If a channel requires its own code, keep a mapping table at the center.
• Source your barcodes from GS1. GTIN/EAN barcodes come from GS1; in Türkiye, GS1 is represented by TOBB. Amazon requires a GTIN in most categories when you create a new product page.

We explained the difference between barcodes and SKUs in detail in our articles what are barcodes, GTIN and EAN and what is a SKU.

Step 2: Set rules for stock movements

The reliability of shared stock depends on it being clear which event changes stock and when.

Deduct at the moment of order

Deduct stock when the order is created, not when you hand it to the carrier. Hours can pass between order and shipment; during that time, stock that hasn't been deducted gets sold again on another channel. Also make sure the same order isn't deducted twice: when an order is split into multiple packages or the order data is pulled again, only one deduction should be made. Recording each deduction with its order number is a sufficient check for this.

Add back on cancellation and return

• Cancellation before shipment: Since the product never left the warehouse, the deducted quantity is added back immediately.
• Return (right of withdrawal, cayma hakkı): In a distance sale, the consumer can withdraw without giving a reason within 14 days of receiving the goods. Inspect the returned product first, and add it back to stock only if it's in sellable condition. Record a damaged product with a separate shrinkage movement.
• Undeliverable shipment: When it comes back to the warehouse, it's inspected and added to stock.

Movement log

Record every stock change along with its reason. Hunting for a discrepancy without knowing why the count changed takes hours.

Step 3: Safety stock, channel caps and threshold alerts

Shared stock reduces delays but doesn't eliminate them. Updates can take longer to reach all channels during busy periods. You can manage this risk with three settings:

• Safety stock: Keep the last few units hidden from your channels. For example, when there are 5 units at the center, 4 are shown on channels. Raising the buffer on campaign and sale days makes sense.
• Per-channel cap: Limit the maximum quantity shown on a channel. When you put a product into a heavy campaign on one channel, you still leave stock for the other channels.
• Threshold alert: Get an alert when stock drops below the level you set. Set the threshold no lower than the number of units you'll sell during your supply or production lead time.

Why might you keep prices separate?

Keeping stock shared doesn't mean you have to keep prices shared too. Many sellers manage stock centrally while setting prices separately on each channel:

• Commission rates can vary by marketplace.
• Shipping agreements and volumetric weight (desi) prices vary from channel to channel.
• Campaign and coupon costs are shared differently on each platform.
• Competition with other sellers offering the same product differs on each channel; price is one of the factors that determine the featured seller. For details, see our article what is the buybox.

If you keep prices separate, calculate your profit per channel as well; the same product can be profitable on one marketplace and loss-making on another. You'll find the components of the calculation in our article calculating profit on marketplaces.

API delays and marketplace stock update limits

Stock is sent to channels through marketplaces' APIs, and the process isn't instantaneous:

• Request limits: Marketplaces cap the number of requests that can be sent to their APIs within a given period. Updating thousands of products one by one can hit this limit; bulk update methods that send multiple products in a single request should be preferred.
• Processing time: A submitted update can take time to appear on the storefront. Some services may accept the request and process it in the background, so you need to separately verify that the update was actually applied.
• Channel errors: A temporary error on one channel shouldn't stop the other channels from being updated. A failed update should be logged and retried.
• Changing rules: Marketplaces regularly update their APIs and retire old services. For example, Trendyol announced that its old order service will be retired on October 15, 2026, and that migration to the new version is required.

Current limits vary by platform and service; check the exact values in each marketplace's developer documentation. That's why we don't give numbers here.

Counting and reconciliation

Even a well-built shared stock setup can drift away from physical stock over time. You can prevent this with three habits:

• Periodic counts: Count fast-moving products often and slow-moving ones less often. Record count discrepancies with a "count adjustment" movement; don't just overwrite the number and move on.
• Channel–center comparison: Regularly compare the stock count on each channel with the center and sort the results into three groups: match, discrepancy, error. If there's a discrepancy, align the channel using the center as the reference; if there's an error, investigate the cause (unmatched barcode, inactive listing, API error).
• Verify the center before syncing: A bulk sync writes the center's count to every channel. If the center is wrong, the error spreads to every channel too.

As the number of channels grows, running these checks manually gets harder; that's why many sellers use integration software that handles stock synchronization. Whichever method you choose, the rules above stay the same.

Shared stock setup checklist

1. List all the channels you sell on and the active listings on each one.
2. Gather all products at the variant level in a single table.
3. Verify each variant's unique barcode and SKU; fix duplicate or empty barcodes.
4. Map channel listings to the records at the center; collect unmatched listings in a separate list.
5. Do a physical count and enter the center's quantities based on the count results.
6. Define stock movement types and who can enter which movement.
7. Put the rules for deducting at the moment of order and adding back on cancellation and return in writing.
8. Set safety stock, channel cap and threshold values by product group.
9. Sync all channels to the center's count and check the result with a channel–center comparison.
10. Monitor discrepancies daily in the first week, then weekly.

Checks to run regularly after setup:

Common mistakes

• Deducting stock at shipment: In the time between order and shipment, the same product sells on another channel.
• Using the same barcode for multiple variants: A sale of one size is deducted from another size's stock.
• Restocking returns without inspecting them: A damaged product goes back on sale, leading to a second return.
• Bulk syncing without verifying the center: The wrong count is written to every channel.
• Changing stock manually in a panel after shared stock is set up: A change made in the panel isn't visible at the center; it gets wiped out at the next sync or causes a lasting discrepancy.

You can find our other articles on products and inventory in the Product and Inventory Management category.