i know what you mean and i have doen that, i have a sandy jill that i thought was less use than a chocolate fireguard, never bothered would bypass rabbits but its sister is a hell of a worker, finding rabbits other have missed. i persevered with this when i wanted to pts sometimes, but one day it just clicked, it found a rabbi, stayed with it scratching it like hell until dug to, all of a sudden she knew her job. im not saying kill all ferrets that dont go down first time, but dont pass on a shit one, in the end its kinder to kill it