And something completely lost on many is a BFR is NOT an exam, it's a REVIEW that should remedy bad habits picked up in the previous two years.
You can't fail a BFR, you can, at worst, be found not up to the task and the instructor won't sign your log book.
In that case either lift your game or find a more friendly instructor. A lot of this is determined of course by whether or not you are using the instructor's aircraft and more than likely is on a VDO switch. (Oh yes, this happens).
I must qualify this by saying I have been ripped off by instructors who own flying organisations who having seen my turbo engine experience had me do a 10 minute run down and mag checks in an O-320 engine.
However one day in the cold high "boonies", I had a mag failure, (enroute I would say), and I shut down without doing same.
The result was a large cost to get a LAME to and from the scene of my perceiveed incompetence.
What did I learn?
Quick mag check and don't go near the snow in winter.
The moral. You have to do one, so learn from it, that's what it was designed for.