I am not sure if I agree with that but not knowing the history means alot. There are time when you just do not have a good animal. I have been fortunate.
I have two little midget house dogs. Got the first when my daughter was little. I always blew into her face (just knowing what a kid would do) it has no effect on her, but she kisses back. Stuff like that makes a HUGE differnce when it comes to pets and little kids.
Years later I bought a Jack Russel from a breeder in Olympia Washington. We flew there from Houston. Same deal, didn't let me see any of the adult dogs, I fell for it again. Brought home the dog, 6 weeks old. he slept under the covers at my feet his whole life. Bit his first child when he was 6 months old, got worse as he got older. Finally when he was 13 he was so out of control I had to put him down.
I have had 15 Jack Russels in the last 18 years and never had a bad one since. I have had lots of other dogs during the same time and none of them have been mean.
There ARE bad dogs that were never mistreated.