Allow requesters to review the interpreter. By default every appointment is a good review. If a requester takes the time to review an interpreter it means the interpreter has done something wrong.
Since only 1/3 of appointments are late due to the interpreter the status column is not a good place to quantify late assignment, the review area should have a interpreter late flag.
Blacklist by Appointment using the review question that would be in the notes area of an appointment: I don't want this interpreter coming back because  (Blacklist flag)
Display the blacklisting in a requester reviewable reviews area. Allow for the blacklist to be lifted - don't delete the note the requester wrote.
Send an email to the agency when an interpreter has been reviewed. Make all reviews visible by interpreter in the interpreter users area.