Question

What could you do to determine whether the outliers in model 2 are authentic measurements?

Answer 1

To determine if a measurement is authentic, you can check whether the measurement makes sense in the context of whatever is being measured. If a measurement is physically impossible, then it is not authentic. If a measurement is inconsistent or far off from multiple repeated measurements of the same kind, then it is not likely to be authentic, so you could test the authenticity by repeating the measurements.