Option to Lock or Grey Out Item-Level Discounts for Salesmen

Here is what happened: one of my salesmen created an invoice where he applied a 100% discount to a single item but billed the rest of the items correctly. Because of this, the total bill looked completely normal at first glance, but there was a hidden mistake. What should I do now?

I would love to ask you if there is a way that you can grey out or lock it for salesmen without editing