Community opinion has split on this one - we have "custom development" and "workflows" options. And probably both are correct. :-)
It is possible to setup a workflow for this kind of scenario, but devil is in the details, and we don't know all the details of the task you have at hand.
Create a new workflow from a template, select the "Sales Order Approval Workflow". You can tweak the parameters to filter orders where Bill-to or Ship-to Country Code is Slovenia and lines include "Item A" in quantity exceeding 50 pcs. So you can set it up to automatically reject any orders within the filter and approve everything else.
So far so good. But this is only one country and one item. If these conditions must apply to hundreds of items in a dozen different countries, you'll have to set up a separate workflow for each of them. Probably not a configuration you want to implement and maintain. In this case it will be a customisation.
