As a politician, the FIRST and FOREMOST responsibility is to represent and serve the people.
A politician should be striving to help the PEOPLE, not him/herself.
Anyone who has worked in an office environment will be able describe what a conflict of interest is.
That being said, if a candidate is found to serve only his or her private interests, rather than the interests of the people as a whole, then there's likely a conflict of interest at play.
Any oath of office should be ENFORCED, so as to ensure personal priorities never trump the person's priority to the people.