Selling on eBay and Shopify? Your Inventory Is Double-Counted and You Don't Know It

The Overselling Disaster#

Tom sells refurbished electronics. He sources 10 units of a Sony headphone model. He lists all 10 on eBay (£85 each) and all 10 on Shopify (£89 each). He figures: if eBay sells 6, Shopify sells 4 — great, all 10 sold. Reality: It's a Friday. A popular tech YouTuber mentions the headphone. eBay sells 8 units in 3 hours. Shopify sells 6 units in the same window. Tom has sold 14 units. He only has 10. He has to cancel 4 orders. Four customers get "sorry, out of stock" emails. Two leave negative feedback on eBay (ratings drop: 97.8% → 96.1%). One files a PayPal dispute (Shopify order). Tom refunds everyone. He's lost: potential £340 in revenue, eBay seller status (reduced visibility in search results for 30 days), customer trust, and 4 hours of his evening dealing with complaints. This happens to every multichannel seller without real-time inventory sync. AskBiz prevents it.

Why eBay and Shopify Don't Sync Natively#

eBay and Shopify are competitors. Neither has an incentive to build seamless native inventory sync to the other. Shopify has its own "Shopify Markets" for multichannel — it integrates with Facebook, Google, and Pinterest natively. eBay integration requires a third-party app. Many sellers use manual workarounds: update eBay listing quantity after every Shopify sale (and vice versa). This works when sales are slow. When 8 eBay orders come in within an hour, the manual update can't keep up. The lag period — even 30 minutes — is enough for overselling to occur. The right solution: a central inventory system that updates all channels simultaneously when any sale occurs.

AskBiz Multichannel Inventory Sync#

AskBiz connects to eBay Seller Hub API and Shopify API simultaneously. When a product sells on either channel: (1) AskBiz receives the sale notification within 60 seconds. (2) Available inventory is decremented across all connected channels. (3) If remaining inventory hits zero, the eBay listing is ended (or set to "out of stock") and the Shopify product is marked out-of-stock automatically. (4) When Tom restocks — he receives 15 more headphone units and updates inventory in AskBiz — all channels update simultaneously. No manual eBay listing edits. No risk of showing available stock that doesn't exist. For Tom's electronics business: zero overselling incidents in 6 months after implementing AskBiz. eBay rating recovered to 99.1% within 60 days.

Multichannel Profitability: eBay vs. Shopify#

Beyond inventory sync, AskBiz provides a side-by-side profitability comparison: eBay vs. Shopify for the same products. eBay: £85 sale price. eBay final value fee: 12.55% = £10.67. Shipping label (integrated): £4.20. COGS: £40. Net profit: £30.13 (35.4%). Shopify: £89 sale price. Shopify payment fee: 2.6% = £2.31. Shipping: £4.20. COGS: £40. Net profit: £42.49 (47.7%). Shopify is significantly more profitable per unit. But eBay drives higher volume (the platform has 132 million active buyers). AskBiz shows which channel delivers more total profit — not just per-unit margin. This lets Tom decide: should he invest in eBay SEO (promoted listings) or Shopify SEO/ads? The answer isn't obvious without channel profit data.

Amazon, eBay, and Shopify: Triple-Channel Management#

Many sellers operate all three: Amazon, eBay, and Shopify. Inventory management becomes exponentially more complex. AskBiz connects all three channels plus any physical POS (if the seller also has a shop or market stall). Central inventory pool: 100 units. Amazon FBA allocation: 40 units (sent to Amazon warehouse). eBay available: from remaining 60 units. Shopify available: from remaining 60 units (shared pool with eBay). When eBay sells 5, Shopify's available quantity drops to 55. When Shopify sells 3, eBay's available quantity drops to 52. Amazon FBA runs independently (Amazon manages its own stock of the 40 units). When Amazon FBA inventory hits 8 units, AskBiz alerts: "Send replenishment to Amazon FBA — current stock 8 units, velocity 3 units/day, 2.7 days of stock remaining."

Inventory Costing Across Channels#

Multichannel inventory also creates accounting complexity. If Tom buys 50 units at £40 COGS, sells 20 on eBay at £85, 15 on Shopify at £89, and 10 on Amazon at £95 — what's his inventory valuation for the remaining 5 units? Under FIFO or weighted average cost, the answer is straightforward: £40 per unit. But if he sourced different batches at different costs (£38, £40, £43), the costing per channel gets complex. AskBiz tracks COGS by purchase batch and allocates it correctly when items sell on each channel. This syncs to Xero/QuickBooks automatically — no manual journal entries for multichannel cost-of-goods. At year-end, the inventory valuation is accurate, channel profitability is correct, and the accountant doesn't spend 3 days reconciling spreadsheets.

• You have 10 units of a product.
• You list all 10 on eBay and all 10 on Shopify simultaneously.
• eBay sells 8.