Is there a way to speed up karma's justice for those who feel wronged in family situations?

What's the best way to communicate to a grandparent that their new partner or situation makes you uncomfortable leaving your child with them?
What's the best way for parents to teach their children empathy when they themselves make insensitive comments in sensitive situations?
Do you think it's fair to buy a valuable item from someone who doesn’t know its true value, or should you inform them before purchasing?