How to stop overselling cards when you list on more than one marketplace
Overselling is the tax you pay for listing the same copy in two places. It costs a refund, a cancellation defect on eBay and a buyer who remembers. Here is why it happens even to careful sellers and how to make it structurally impossible.
How an oversell actually happens
You own one Near Mint copy. It is listed on eBay and on your Shopify store. On Saturday night both buyers check out within the same hour. Neither marketplace knows about the other, so both accept. Sunday morning you have two orders and one card. Even a seller who updates quantities by hand every morning has a window of hours every day in which this can occur, and the window is widest exactly when sales are busiest.
Three separate problems hide in that story: the two marketplaces hold separate copies of the truth, nothing tells one marketplace about a sale on the other, and nothing checks afterwards whether the numbers still match.
1. One inventory, not one per marketplace
The marketplaces should be views of a single stock list, not stock lists of their own. Every copy you own is one row with a quantity, and each marketplace listing is a projection of that row. When the row changes, the projections change. This is the difference between an inventory tool and a listing tool: a listing tool helps you create listings quickly, an inventory tool owns the count.
In LGSTome, publishing is exactly this projection. You pick Shopify, Mana Pool or eBay and the marketplace is brought in line with the inventory: creates, updates and removals are computed from the difference and shown to you before they are sent.
2. Cross-delisting the moment a sale lands
Marketplaces tell you about sales by webhook, usually within seconds of checkout. That is the moment to act. When a Shopify order arrives, the sold copies are subtracted from inventory and, because inventory now has fewer copies than the eBay and Mana Pool listings advertise, those listings are reduced or withdrawn immediately. The same runs in every direction.
3. A drift audit for everything else
Webhooks get missed. A marketplace has an outage, a listing is edited by hand in the marketplace’s own dashboard, or a push half-succeeds. The only defence is to read back what each marketplace actually advertises and compare it with what you own.
| Marketplace says | You own | Kind | What to do |
|---|---|---|---|
| 3 | 2 | Oversell | Correct the marketplace down to 2 immediately. This is the dangerous one. |
| 1 | 2 | Under-listing | You are leaving a sale on the table; fix on the next push. |
| no listing | 2 | Missing | Usually stock at the wrong location or a failed push; investigate. |
LGSTome runs this audit after every push and once a day. Oversells are corrected automatically. Under-listings are recorded for you to review and reconcile on the next publish, because reducing a sale opportunity is never as urgent as preventing a double sale.
Habits that still matter
- Never edit quantities inside a marketplace’s own dashboard once a tool owns the inventory. Change the inventory and republish.
- Keep in-store sales in the same inventory. A Shopify POS sale of a single is a sale like any other; if it bypasses the inventory, online listings drift.
- When two orders for one copy do collide, refund the later one quickly and explain. Marketplaces track cancellation rates, and speed is the only thing you control after the fact.
Try this with your own binder. LGSTome is free for your first 1,000 cards.
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