I had a teacup chihuahua that would not train for me. I tried for the better part of 8 YEARS, and he just would not stop some of his bad behaviours. I gave him to my GF, and he responded to her nearly instantly, and is a very well-behaved little gentleman. He needed a small pack to blend in with, and when I lost my other dog the chi went stupid-er.
Someone I know admired my Dobe service dogs and got one for herself.
Had him for almost two years and he was really biting her.
*Hard*.
She spent a fortune on medical tests, behavioral and obedience training and he still bit her.
She gave him to another woman and they live happily now.
Sometimes, a dog just does not like something about you...although I have never experienced that myself, I’m an irresistible mutt magnet. :)
[and she was not really a A Dobe Person, anyway. we’re “different”]