I understand what you are saying. I’ve been lucky most of the time in that respect, the exception being our beloved Lucy, who we mourn to this day, and always will.
I learned a lot from the purchase of the mean JRT. The breeder would not let me see any of her adult dogs, I suspect because they were too mean for me to handle. My JRT bit his first person when he (the dog) was 5 months old. I had to watch him closely and keep him away from people his entire life. I’ll never keep a dog like that again.