Thanks Jason - I took a look at Customize > Entities > Order > Fields
"Request Taker" has a Name and Schema Name of "new_salesperson". The Description is "Salesperson associated with an order." "new_" may be a prefix used to denote custom entity fields in this organization. I'm guessing this isn't a native CRM naming convention. The State of this field is Unmanaged (like the rest of the "new_") fields in this table.
Is an "Unmanaged" field State really the key indicator that the field is custom and not native to CRM?