No bad dogs only bad owners is a load of bull, if its not in there you can't put it in.
If you wanted a dog for herding sheep, digging to, coursing with, a gundog, a guard dog etc etc would you go to Crufts and pick the dog that conforms to the breed standard, or pick the one down the street because its closest and hes soooo cute, or have a look in the free ads or look for a proven worker?
Buy from untested stock and you may get lucky but dogs need to be fed, trained and looked after for up to 15 years so why increase your odds of getting a duff one?????????????