It doesn't surprise me that horses may behave in one way at a dealers yard when in full work with professionals riding, and then their behaviour changes once in a novice riders hands.
True enough - but I imagine that Safecobs, by their own use of a grading system of suitability, very often ARE selling as suitable for a novice thereby giving the novice a false impression of how the horse might be when it has left their yard and is being cared for and ridden by the unsuspecting novice.
This is what i wanted to say but you have put it better