I know that what I am about to suggest may not be very practical but I strongly feel all check airmen need to undergo psychological testing or assessment to ascertain whether they are genuinely up to the task.
In my younger days as a lowly first officer, I had come across many specimens who might be great machine operators but absolutely lacking in people skills. However due to old boy's networking they were made checkers making life really miserable for those not of their mindset or skin colour.
This does not mean we should take political correctness to the extreme. However, those gungho kick ass type certainly have no place in the check and training department in any professional set up.