What’s tricky is that if the shop responds to inventoryUpdated when confirming a transaction, you’re likely to crash the game entirely…
inventoryUpdated already creates a bit of a nightmare when buying and selling large quantities of items (especially big stacks) because each individual item in a transaction with Inventory triggers inventoryUpdated, which destroys and rebuilds the InventorySlotUI objects, leading to excess garbage collection. I crafted a solution for that issue here: Big problems with how UI is being redrawn - #6 by Brian_Trotter
In terms of crafting a solution for the inventory changing while the shop window is open, I’ll have to take a look at this over the weekend. One simple solution might be to subscribe to inventoryUpdated (to have it redraw the shop window), but at the beginning of ConfirmTransaction, unsubscribe from the event (to prevent a potentially cataclysm) and re-subscribing at the end of ConfirmTransaction… but… there are some things that need to be factored in (for example: If I have something set to sell, but I equip it before confirming, then that needs to be backed out).