Answer to a question posed by Scott Rigby about keeping the names of people phoning because their instructor has let them down.
A couple of years ago my wife booked in a foreign gentleman who's English was almost none existent. 
I struggled with him for about 10 hourly lessons, had no concept whatsoever about road signs, lines, speed limits. Every question I asked or instruction I gave him the answer was, "yes yes."
Then he got a 100%  pass on his Theory and booked his test. I told him not in my car, still couldn't control the clutch. I know of at least 6 other instructors he called and he must have been going through a list because he even called here another couple of time without I'm sure any idea who he was calling. 
That makes me one of the nasty instructors letting down a pupil who had booked their test.