I’ve experienced that exact same problem for years now. The Shopify Team told us we needed to upgrade to Plus, which we did last week. Now we are still experiencing the same issues, we’re getting no support at all, and we’re stuck into a $24k/year contract.
Quick example of muy problem:
Location A fulfills US & Canada (Market A) only > product X is in stock in that location
Location B fulfills European countries (Market B) only > product X is out of stock in that location
A customer from a European country will see the product X in stock, and will even be allowed to complete checkout, ignoring that there’s no stock in that location.
This is leading us to oversell. Shopify seems to be aware of this problem because they’ve launched this feature > https://help.shopify.com/en/manual/markets/inventory_and_fulfillment. But it’s only for selected merchants and we’re not one of them.
There’s another thread about this topic: https://community.shopify.com/c/international-commerce/inventory-and-fulfillment-with-markets/m-p/1969097#M3547