How to deal with a difficult DE?

I have a touchy issue I need guidance on..

Without going into any specifics, how can I advise a student of mine
about problems he/she is facing while working with a Designated Pilot
Examiner towards a rating? Seem this particular DE is using
'questionable' tactics and being unnecessarily difficult with dealing
with this student?

Should I advise the student to voice their concerns towards the DE or
contact the local FSDO? From information I have gathered from other
instructors and students in my area, they all agree that this DE is
not using standard evaluation methods.

What would be involved if this student decides to stop the test and
switch to another DE?

Sorry I can be more specific.