When a trend line is drawn on a scatter-plot there are 4 points above the trend line about how many points should be below the trend line?

The amount an individual point departs from the trend line is the important feature, not that the number above and below should be balanced.

A point that is much further away from the trend line is less likely to represent the process being plotted.

Each point is of course quite real, but each are influenced by measurement error, random processes within the experiment, recording (transcription) error, and so on.

If most of your points lie on a smooth curve, it is more likely that an outlier is subject to error.