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keep your nose clean
To behave well and avoid trouble. [INFORMAL]
lay/put your cards on the table
To tell someone the truth about your feelings, opinions, or plans.
a level playing field
A situation that is fair and where no one has an advantage over other people.
move the goalposts
To change the rules or aims in a situation to gain an advantage or make things more difficult for others.
on the level
Honest or true.
stab sb in the back
To secretly do something that hurts and betrays someone you trust.
say sth to sb’s face
To say something, especially something critical or unpleasant, directly to the person.
above board
Honest and legal.
not beat around/about the bush
To say what you want to say clearly and directly.
below the belt
Cruel and unfair.
by fair means or foul
To achieve something using any possible method, even if it’s dishonest or unfair.
come clean
To tell the truth about something.
fair and square
To do something honestly and without cheating.