Wow! and I used to get the chop for thread drift? less vitriol, amigos!
A good instructor has a reasonable acquaintance with the aircraft, not necessarily intimate. A good instructor is able to assess the qualities of his student. And a very very good instructor does not hesitate to say "I have control!" when things get too exciting.
The more experience you have as an instructor, the higher your pain barrier and the closer one can come to that coffin corner before taking over; but one's hands are never too far away. When at the age of 50 I first took up flying, and wanted to learn how to land, John Cumberpatch at a strip in the US of A which enjoyed a perpetual crosswind, never let me contact the earth. Which now makes me wonder how experienced he actually was?........
There are types of aircraft of which few examples exist, usually for very good reasons. And then some bozo actually buys it because it is cheap (for very good reasons) and asks an instructor to help him learn to fly the beast.....
Can any of you wise old birds reading this titilate us with an example from your experience of this problem?