Updating database inventory

I have heard people removing inteventory (Qty) when an item has been purchased, but not during 'add' or 'remove' from cart.

I understand that it may be due to multiple people purchasing at once. If your creditcard authorization does "Capture & Authorize", then you may look into just authorizing, and batch charge at the end-of-the-day, so you don't get extra fees when you need to cancel a charge.