How to fetch custom fileld values of Orders?

what is the proper way of getiing custom field values of an Order? I have ‘Sales_Person’ text field associated with each Order (or Job? btw is this the same thing?), and want to retrieve it’s value.
I tried crm/rest/v1/orders/someId?optional_properties=custom_fields for no avail. Could anybody give me some clues? Either REST or XML-RPC way will be good.

Yes, legacy naming for XMLRPC has Jobs = Orders, although in REST they are just Orders.

We do not currently have Custom Field support in REST for Orders, although it is on our roadmap.

If you specify the field prefixed by an underscore ("_customFieldName") in the XMLRPC query to the DataService Jobs table, you should be able to get the current value for a given record.