Before we get started here, let me preface this post by outlining my order of operations here

Customer orders part over the phone, Create Sales order, Convert to invoice, Apply credit card payment, Fulfill order.

The problem im running into lately is, if the customer calls back between the "apply credit card payment to invoice" step, and the "fulfill order through warehouse" step...asking to cancel an item, change their order, etc... Anything I do to try to accomplish this results in an upwards impact of inventory, that should not be happening.

In the case outlined above, the parts have not been fulfilled yet, they havent left inventory.