Quality of earnings

Are the profits real.

Signals

Compare cash from operations with net profit over several years. A persistent gap, growing receivables or inventory, and frequent one-off items all suggest earnings flattered by choices.

Revenue recognised early is the most common aggressive choice.
Capitalising costs moves them off the income statement and into assets.

Consistency

A company changing accounting policy, year end, or segment definitions repeatedly makes comparison hard, which is sometimes the point.