This was always an issue in Rome. People were afraid their heirs would turn out to secretly be wannabe dictators, and you couldn’t do anything about it since you were dead. How would you go about making sure your heir was as close to your vision as possible, both outwardly and in their desires should they be emperor?
I would hope you would pick someone you know well enough to feel comfortable with them taking over.
Of course, power corrupts even the most well intentioned, so there’s always a chance, but you can’t predict that no matter what games you play.