Careful selection should overcome 99% of the problem imo. Fair to say we all make mistakes now and again but in general with the right training and nurturing most dogs will come good.
Army selection is a prime example. Bunch of sixteen year old kids apply to join up, careful selection by experienced people should ensure that only suitable candidates are chosen and with the right training they go on to be hero's......just my opinion!
iv tried one dog in particular ,had him from 8 months ,started him on rats brought him to watch digs gave him rags and he still walked fron an occupied ear