From business perspective, in call center it should be possible to applied a total discount for the order if there are mixed sales and return lines. An example is if item should be replaced or exchanged in the same order, currently this escenario isn't possible, so users must make a separately return if a total discount is to be applied to an order.  

Needs Votes
Ideas Administrator

Thanks for the feature suggestion. For the time being, please consider using line discount to achieve the goal. We will continue to monitor the votes to determine its consideration on our feature roadmap. - Boyce Zhu, Principal Product Manager for Dynamics 365 Commerce