If you sell in the shop, at shows, on eBay and online, you will eventually sell the same card twice. It is not carelessness — it is arithmetic.
Why it happens
Each channel keeps its own count. A card sells at the counter on Saturday; the eBay listing is still live on Sunday. Someone buys it. You now have to cancel, refund and apologise, and eBay records a defect against your account.
Manual reconciliation does not solve this. It just moves the failure to whenever you last had time to reconcile.
The partial fixes, and their limits
- Reconciling nightly — better, but a card can still double-sell within a day, and the work never ends.
- Listing only some stock online — safe, but you are deliberately not selling most of your inventory.
- Separate stock for each channel — no overselling, but you are holding several times the inventory and each pool is thinner.
The structural fix
One stock count that every channel decrements. A card is allocated to exactly one channel at a time, and when it sells anywhere, it is gone everywhere.
That is how The TCG OS is built: intake, then allocation to a single channel — shop, a show, or eBay — with premium singles QR-tagged so the physical card and the record cannot drift apart. A sale on any channel updates the others immediately, so there is no reconciliation step to forget.
The mechanics are documented in the vendor guide: allocation, channels and eBay.