Checking if you want to assign the 'best answer'

As members can’t unassign a best answer when it’s been assigned, even if they’ve just clicked it in error, this feature request is basically a thing that comes up which says Are you sure you'd like to mark this as the best answer? With the option to turn the prompt on/off of course (best default to off).  

I’ve had a few examples of a best answer that wasn’t a best answer and wasn’t meant to be...