What does Mr. Buckingham mean when he says, "Nine chances out of ten, it's wrong and you really shouldn't be there?" Who is he talking about where they should be instead?

Nine chances out of ten, it's wrong means that 90% of the time, the place the person is, or wants to go is a wrong judgment that only has 10% chance of being a good option. This means that the probability of been wrong is 9/10 which is very high.

Mr Buckingham is trying to tell them to be somewhere else that 90% more probable of being a good option so as to maximize their decision making.

youll get beat if you dont listen to the older parental figures rules