we’re running a travel / ticketing agency, where all of the items are non-inventory and rates are not fixed.
it’s an issue to trace underpriced sale invoices.
Example: invoice purchased for aed 1000 and by mistake invoiced 500 aed to a customer.
is there anyway to trace it …?
No. And it makes no difference whether the line item is for an inventory or non-inventory item or an undefined good or service. Or whether there is a predetermined cost or price. You can sell anything for any price, at a profit or at a loss.
But have you considered using billable expenses? That way, the default price is what you paid for something. You can then mark up the invoice as desired. But nothing will prevent you from selling at a loss.